Phineas Mason was a member of Bestman Salvage, under Adrian Toomes. After the Battle of New York, the Department of Damage Control was founded, which put Bestman Salvage out of business. An vengeful and opportunistic Toomes decided that their crew should steal from Damage Control with the Chitauri tech they were able to salvage. Disappointed because he wanted a chance to work with the tech, Mason agreed to the endeavor.
Mason became the technician in charge of making new weapons and gadgets out of the high-tech equipment Toomes stole from Damage Control and other sources. Among other things, he created Shocker's Vibro-Shock Gauntlets for Jackson Brice and battle suit equipped with two huge mechanical wings for Toomes. His most ambitious project was a high-altitude vacuum seal, which would allow Toomes to enter and rob airplanes while they were airborn.
After being turned down by Toomes multiple times, Toomes finally agreed to let Mason build the seal when Iron Man and the FBI found out about his operations, forcing them to make one final heist before retiring. With the seal, Toomes was able to break into the plane transporting the Avengers' weapons and equipment from Avengers Tower to their new headquarters. The plan was foiled by local hero Spider-Man and Toomes was arrested. It's unknown what became of Mason afterwards.
Trivia
In the comics, Phineas Mason is an elderly technician who started a criminal career after developing an obsession for super-humans, as well as the father of Rick Mason. He aided various criminals, like Kingpin and Blizzard, providing them with new advanced equipment.
