Phineas Flynn, or Phineas-2, is the 2nd Dimension counterpart of Phineas Flynn. Stuck in an area which is ruled by Dr. Heinz Doofenshmirtz, he has grown up without summer vacation, and he never heard about it.
Phineas is presumed to be an optimist, like his 1st Dimension counterpart, though this side of him isn't shown in the film. Speaking of which, he is depicted in the movie as having a need to join The Resistance's movement of overthrowing Doofenshmirtz, only for him and Ferb to be rebuffed by Candace. He also displays a caring attitude, which is usually aimed towards the 1st Dimension characters in the film, as he showed reluctance at allowing Candace to separate their mine cart from theirs, which would result in their capture at the hands of the Norm bots.
Phineas is physically identical to his 1st Dimension counterpart, except that he is paler, has his hair cut military-style, and wears a white shirt and Dooferalls. As a Resistance member, he wears a dark-brown or light-black shirt with a large black collar, black shorts, black boots, dark-gray gloves, a silver shoulder-pad with a strap, and a headband that holds what appears to be a laser weapon and/or communications device.
Phineas and Ferb meet their 1st Dimension counterparts, with the former believing that they are being replaced with duplicates at first. He shares an emotional hug with Perry-1, initially believing he is his Perry before he tells Phineas-1 of the nonexistence of summer in the 2nd Dimension. After Perry-1 departs, the four all decide to go to the house of Isabella for help, during which they are joined by Buford. The five then arrive at the Resistance headquarters via chute, and he, Ferb, and their 1st Dimension selves find out that Candace is the Resistance's leader.
Candace agrees to help Phineas-1, Ferb-1, and a recently-arrived Candace-1 retrieve a captured Perry-1, but tells him and Ferb to stay behind. However, they stow away in the mine carts used by the Resistance to get to Doofenshmirtz Evil Incorporated. When the group manages to rescue Perry-1 and get pursued by Norm bots, Candace is forced to separate the mine cart containing the 1st Dimension characters, resulting in their capture; Phineas protests against this, but he is overridden.
Later managing to get recruited into the Resistance along with Ferb, Phineas arrives at DEI to rescue Candace, who was captured after aiding the 1st Dimension characters. She initially disapproves of her brothers' decisions, but after seeing they can handle themselves, she changes her mind and the three share a loving hug.
Phineas is later among the Resistance members that congratulate the 1st Dimension characters for defeating Doofenshmirtz. He is also reunited with Perry, whose evil was "fried out of him" after a climactic showdown with Perry-1, and he returns to his home dimension with his pet.
In "Tales From the Resistance: Back to the 2nd Dimension", following Doofenshmirtz's arrest, Phineas settled down into a peaceful life with his family, feeling happy that Perry is now back. He and the other kids settled down, reinvigorating their sense of fun towards sports. However, the glee is cut short when two giant insect robots attacked the park and Perry is kidnapped by several animal cyborgs (who happen to be the missing agents of O.W.C.A. during Doofenshmirtz's reign). Phineas later learns from Candace that Doofenshmirtz's ex-wife Charlene was the one responsible for turning the agents into cyborgs and kidnapping Perry, Phineas aids the Resistance into rescuing Perry. He and Perry later aid Candace (and a restrained Doofenshmirtz) into finding Charlene's penthouse, where they learn that Doofenshmirtz and Charlene had pretended to be divorced because of several finance advantages. Plus, Charlene revealed that the park attack and the kidnapping was nothing but a ruse to trick the Resistance into freeing her husband. As such, Charlene sets her animal cyborgs to trap Phineas, Candace, and Perry; in a more darker note, Ferb was supposedly captured by Pandaborg and turned into a cyborg. However, it turns out that Ferb had actually faked being turned into a cyborg and released his siblings and Perry, and Phineas had actually played along as part of their plan for the Resistance to set off a frontal attack in Charlene's penthouse. After the Resistance arrives in Charlene's penthouse, Phineas helps Isabella freeing Chihuahuaborg of his evil programming. Eventually, after the rest of the animal agents are freed from their evil programming (except for Pandaborg), Candace is about to send both Doofenshmirtz and Charlene into custody, only to be interrupted by their daughter Vanessa, who convinces Candace to let her have a moment with her family. As Phineas and Ferb watch Vanessa sharing a moment with her family, Vanessa suddenly takes the opportunity to help her family and Pandaborg to escape in a hover car driven by Vanessa's boyfriend Tony Marzulo. Despite the Doofenshmirtz family's escape, Phineas would still continue settling down to a peaceful life with his family.