- “Well, a brother is a brother, but I couldn't have asked for a better one than Ferb. You know what I mean?”
Ferb is not just Phineas' stepbrother, he is also his best friend. If it wasn't for Ferb, the wild and crazy days that they have together would not happen. Phineas is very kind to Ferb, and he often tells people anything that needs saying (as Ferb doesn't talk much and is more of a "man of action"), such as when Phineas asked Ferb to go to a store, but not before handing him a note with what they wanted on it so that Ferb didn't have to ask.
The two have known each other almost their whole life, and spend almost every second of the day with each other. They carry a strong, loving bond that holds them together through thick and thin.
Perhaps the greatest example of the two's everlasting friendship is when Phineas states that he couldn't ever ask for a better brother than Ferb.
- “You may be a pain, but you are my brother.”
As his older sister and the eldest child of the household, Phineas has always looked up upon Candace. Despite her non-supportive attitude and obsessive behavior, Phineas doesn't display any exasperation for it and rather sees it as excitement. He doesn't take notice of her intentions to get him and Ferb in trouble and is under the impression that Candace is curious about and interested in what they're doing.
Contrary to Candace's perception, he believes what he does is innocent. He isn't worried, irked, or confused when she would yell, "I'm telling mom!" but would sometimes reply quizzically, "Tell her what?". At certain times, he would offer her a prominent role in one of the plans he devises, assuming that she would enjoy it.
However, there was an occasion when Phineas lost his patience with Candace and burst at her after she refused to cooperate with him.
Nonetheless, he admires her and holds her dearly, always willing to help her when she needs it. He treats her very nicely in spite of the fact that she would rarely return the favor. Such instances include when he let her drive a monster truck to boost her driving confidence and volunteered to help Candace get into a Paisley Sideburn Brothers concert.
He helped Candace take the traffic surveillance video disk back from Norm in disregard to that he'd most likely get in trouble with Linda as soon as she'd see its contents. In addition to this, he admired her efforts to contribute to their mother's birthday celebration and recorded her as she rehearsed her song dedicated to Linda.
Furthermore, he tried to cheer her up after she came to believe that Jeremy dumped her, made her a new cellphone to compensate for the loss of another one, and built a hair growth and styling machine to help her restore her hair to its original condition after a disastrous self-haircut. He also gave her some moon-made ice cream for Jeremy after her efforts to cook a meal for Jeremy failed.
Phineas has gone out of his way to save Candace from peril on multiple occasions in disregard of the danger he has confronted himself within the process of doing so.
Though Candace has very rarely been certain to herself being courageous, Phineas has acknowledged that she does possess a degree of bravery. He made this known after she left the safety of their spaceship to retrieve their mom's car and found herself forced to face off against a giant robot in the process. Phineas' love for Candace was further recognized during his birthday when he received a rare sewer maintenance and repair tool from her. He cherished the gift and shared an embrace with Candace, telling her he couldn't possibly have a better sister.
Linda is Phineas's biological mother. He is always polite and honest to her. She never questions the boys because every time they do something, it almost magically disappears, mostly due to Dr. Doofenshmirtz's crazy inventions. Linda seems to think it's all their spectacular imaginations.
He cares for her extremely and has gone to such extents as to making a huge bash for her birthday. He was also very concerned and even a little guilty when he forgot about it.
Both he and Ferb were aware of Linda's past as a pop star named Lindana.
Phineas is very kind to his stepfather and since he's known him as a father all his life, calls him "Dad". Lawrence has come across Phineas and Ferb's schemes, but it does not seem to faze him.
Perry is Phineas and Ferb's pet platypus. When Phineas and Ferb first bought Perry, they originally wanted to name him Bartholomew, but on the ride home from the pet store, they changed it to Perry. Perry goes on different spy missions without either of them knowing. He usually ends up cleaning up their daily plan before Mom gets home. Phineas usually explains that platypi like Perry "don't do much". Phineas appears to care extremely for Perry.
Phineas often wonders where Perry goes when they can't find him, as he asks "Hey, where's Perry?" (or something to that effect). This could be because he wants to make sure he's safe.
In "Oh, There You Are, Perry", Phineas was worried when Perry went missing. He could also recognize Perry from other platypuses even though they all looked the same. This shows the closeness he had with his pet.
In Phineas and Ferb the Movie: Across the 2nd Dimension, Phineas was very affected by the revelation of Perry being a secret agent. He was hurt when Dr. Doofenshmirtz-2 stated that Perry had been using him and his family as a cover. Phineas then becomes furious with Perry as he thought that their friendship was nothing but a lie. He was also disappointed when Perry still decided to go off secretly (although Phineas was unaware that Perry was going to surrender himself to Doofenshmirtz so that he would not hurt the boys) and sadly telling him to go ahead and leave as he lost trust in him. However, he quickly got over it when he found out that Perry was captured by Doofenshmirtz-2 and wanted to save him although he had the chance to go back to his dimension. By the end of the movie, Phineas apologized to Perry, they reconciled and Phineas's faith in Perry was restored as the reason Perry had to hide his identity to prevent being relocated and never see Phineas or Ferb again. He and the rest of his friends even chose to give up their best day ever by erasing that day from their memories (not before hugging goodbye) so that Phineas is able to keep Perry by his side, showing that Perry is extremely important in his life.
Phineas' deep connection with Perry is also explained in "Where's Perry?". In the episode, while hanging on vines with Ferb, Isabella, Buford and Baljeet, Phineas saw Perry down the gorge and insisted on finding him, despite the others saying that Perry was left home and there was no way that Perry could come all the way to Africa. Phineas was worried that Perry could be in danger and said to his friends that Perry is for him more than a pet, but a friend. Phineas kept searching for Perry throughout the whole episode. Near the end of the episode, Phineas finally found Perry and was overjoyed to see his pet again.
Bucky and Phineas seemed to be quite close as evidence by Lawrence trying to protect him from knowing that he was deceased. Bucky got sick and ran off to live on kindly Ol' Simon's Farms.
Phineas is very popular around Maple Drive. The other neighborhood children enjoy his and Ferb's activities, nearly always taking part in them. This is possibly how he met his closer friends.
Phineas normally takes on his activities with a main "circle" of friends. Buford Van Stomm is in this group; in the past, he more so bullied Phineas, though the two became very close friends after some time.
Baljeet is another. He asks for Phineas and Ferb's help regularly, even setting up a "Baljeet signal" hologram for them to speak in needed situations. Phineas helps him happily.
- “Isabella, you're the best!”
- ―Phineas thanking Isabella with a hug[src]
- Main article: Isabella Garcia-Shapiro
It is well known by everyone that Isabella Garcia-Shapiro, the across the street neighbor of Phineas and Ferb, has a huge crush on Phineas. She comes over every day to hang out with him (and Ferb) and help them with their daily projects. Though, despite her occasional flirting, Phineas was completely unaware of her crush on him for many, many years.
Phineas has been shown to exhibit more and more affection toward Isabella as the series has progressed. In "Rollercoaster", he seems to be rather indifferent to her, but in many later episodes, including "Gaming the System", "That Sinking Feeling", "The Beak", and "Phineas and Ferb Summer Belongs to You!", Phineas has been shown to really enjoy her company. The two often dance together, and as Phineas considers Isabella to be one of his closest friends, she is usually the most likely person he will choose to pair up with during team sports and activities, other than Ferb. Phineas also expresses great concern whenever Isabella is in trouble, and the two often rescue each other from dangerous situations.
In Phineas and Ferb the Movie: Across the 2nd Dimension, Phineas appeared to be happily surprised after Isabella kissed him, revealing that he'd likely easily come to return her feelings if they had been allowed to keep their memories of that moment. Though, in "Act Your Age", Phineas openly admits that he didn't consciously start thinking about Isabella in a romantic way until around high school.
During Phineas and Ferb's career as "The Beak"
The only moment (so far) where Isabella truly felt neglected by Phineas and actually doubted her feelings for him is when Phineas and Ferb unexpectedly became the new town superheroes, masquerading as "The Beak".
Isabella wants to interview Phineas and Ferb to get a patch, however, she misses them and has to do an alternate story on The Beak. Who she is unaware is actually Phineas and Ferb. She calls Phineas and was annoyed at him. He decides to tell her about he and Ferb being "The Beak", but is unable to at the time because of Khaka Peu Peu's interruption. When "The Beak" is laying powered down after being slammed into a building during this time, Phineas hears Isabella say "Where's Phineas? He'd know what to do!" The Beak Powers up and continues to fight. Khaka Peü Peü then tells Phineas that he will get him through what's most important to him. This causes Phineas to remark that they can't tell Isabella that they are the Beak now because it would put her in danger, implying that he considers Isabella important to him. It could be believed that Phineas really cares about Isabella. Isabella swoons for "The Beak" many times during "The Beak's Theme Song", not realizing that it was still Phineas she was swooning for.
Isabella is upset and confused as to why Phineas keeps rejecting her and disappearing when she needs him. When Isabella climbs atop City Hall to take pictures, "The Beak" slams into the building, knocking her over the edge. Khaka Peü Peü then knocks a Bango-Ru billboard off an adjacent building leaving Phineas the dilemma of saving Isabella as she clings to the side of the building, slowly losing her grip, or saving the bystanders from the billboard. This is until Phineas jumps out of the suit and grabs her hand before she falls, leaving Ferb to dispatch the billboard. Later, Phineas then reveals that he was the Beak to her and apologizes for not telling her. She realizes that Phineas was just trying to protect her, and apologizes for doubting him. She flirts with Phineas, in the end, saying he's really brave. To which Phineas responds by noting she was brave too.
During their trip around the world
During their trip around the world, Isabella tries to get Phineas to get in the spirit of being in the "City of Love", but he is focused on using the stop in Paris to repair the plane. She expresses her feelings in a song, a bit despondent that Phineas is oblivious to the romantic nature of the city. When Phineas points out to Ferb that he thought he and Vanessa would avail themselves of romantic nature of Paris, Isabella becomes extremely frustrated that he missed the point, snapping a pencil in the process. She then imagines her own head exploding when Phineas does the same with Candace about her and Jeremy, causing Phineas a small amount of distress and/or puzzlement.
On their way back to Danville, the Baguette Boat falls completely apart, and they crash land on a deserted island with only a "big fat ox" for company. Desperate for a way off the island, all the while gradually losing his cool, Phineas digs a huge hole in the sand in search for something useful. Buford's taunts don't help him. Isabella goes off alone and cries. Ferb walks up to her and hands her a handkerchief. Then she pours out her heart to Ferb, sobbing that she and Phineas were together in Paris and he didn't even notice her. She feels like giving up and complains he won't even do something as simple as enjoying the beautiful sunset with her. At this moment Phineas runs up to her and suggests that they could build a tunnel under the ocean. He doesn't attempt this and instead he gives up, sits to the ground and says they can at least enjoy the beautiful sunset. Isabella sees that Phineas' spirit is broken, and something clicks in her head. She realizes that this wasn't the spectacular, confident boy she fell in love with and tells him angrily that he can't enjoy the sunset because giving up wasn't part of his plan. Isabella reminds him of everything he did in his life, almost confessing about her crush on him. She then mentions Ferb's map, starting to say that giving up wasn't part of the plan he marked out on it. Inspired, he cuts her off and hugs her, leaving her in a sort of trance. He then leaves her to get to work on their way to get off the island.
Back in Danville, with only a second to spare, they make it just in time to beat the sun, and the other Fireside Girls have a welcome home party ready for them. Isabella hugs Phineas from behind, saying "You guys are amazing!". In response to this, Phineas holds her hands, looks back and smiles. A musical number breaks out, and Isabella and Phineas dance and sing a duet, "Summer Belongs to You". Phineas often reaches over to hold her hand throughout the song and it seems he becomes even more comfortable around her.
Ten Years Later
After years of having Phineas not notice her, Isabella eventually gave up the idea of ever getting into a relationship with him, despite not being able to get over him. Early on in high school, Phineas started to develop romantic feelings towards her too, though as he was unaware that she had ever had a crush on him, he kept his feelings a secret, thinking his love for her would be unrequited.
After high school, Isabella became very busy and stopped visiting Phineas and Ferb in their backyard. During this time, Phineas began to realize how lonely he felt without her around. Eventually, Baljeet and Buford told Phineas directly about Isabella's crush on him, and he resolved to track her down to admit his feelings to her before she left for college. He eventually found her in front of his house, where she had been waiting to say goodbye to him before leaving. There, Phineas revealed to Isabella that Baljeet had told him about her crush, which she admitted to. Phineas then admits himself that he has had a crush on her ever since high school. After sadly contemplating the bad timing of their respective crushes on each other, the two finally came to a conclusion: Phineas decided that he would attend the same college as Isabella, Tri-State State, so they could begin a romantic relationship together. Isabella happily agreed to this, and the two embraced. Moments after she had driven away, Phineas impulsively accepted a ride from Vanessa and Ferb to catch up to Isabella at a stoplight and kiss her for the first time. The two become a couple as young adults during their college years and presumably stay together after.
For a long time, Phineas had no idea that his pet platypus Perry had the continuous mission to fight the evil Dr. Doofenshmirtz and prevent him from taking over the Tri-State Area. For that reason, he was completely unaware that Dr. Doofenshmirtz even existed, although he has been the reason for several weird things that have happened in Phineas' life (For example, Doofenshmirtz is very often the cause of the disappearance of Phineas and Ferb's inventions).
Phineas first personally met Dr. Doofenshmirtz when he and Ferb unwittingly crashed into his Other-Dimensionator. After that, the boys excused themselves, strikes up an acquaintance with Doofenshmirtz and even repaired the Other-Dimensionator for him (and made it work). Phineas showed some respect for Doofenshmirtz as an inventive "elderly" at the beginning, but that seemed to change after he discovered that Doofenshmirtz was not a harmless pharmacist, but an evil scientist. He was even mad at Perry for not warning him about Doofenshmirtz. In spite of this, Phineas does help Doofenshmirtz escape from executed by a Goozim after his 2nd Dimension counterpart betrayed him.
However, Doofenshmirtz acted very friendly towards Phineas and Ferb for the whole movie. He referred to them as "fellas" and even seemed to care for them. He seemed shocked when the 2nd Dimension Doofenshmirtz gave his General Perry The Platyborg the command to hurt the boys. Later, he even helped them stop the Norm Bots invasion caused by his alternate counterpart, even going so far to save him, Ferb, and Perry from being killed by 2nd Dimension Doofenshmirtz by ordering the latter to stop. After the invasion, Phineas and Doofenshmirtz completely forgot about each other, due to the Amnesia-inator of the O.W.C.A.