So, Phineas and Ferb basically went back to the 70s (or that Bio Dad went to the 2010s). In here, he’s Perry the Platypus as a human boy. He loves spy fiction, and he wants to be a spy himself. So he created some gadgets he finds interesting from a couple of spy fiction and used them to have fun.
Phineas likes him despite that he’s his biological father because he creates awesome but practical stuff. Not to mention he knows martial arts himself (referring to Bio Dad, obviously).