Phineas and Ferb Season 4 Episode 19 - Happy Birthday, Isabella Episode Title: Happy Birthday, Isabella Episode Description: It's Isabella's birthday, and Phineas and the gang celebrate it in a big way, complete with a giant cake and piñatas. To Isabella however, all she really wants is to be alone with Phineas, but she keeps missing by a second. Meanwhile, Doofenshmirtz installs his Bugs Me-Inator onto an evil bug bus and drives around Danville turning all the things that bug him literally into bugs, and Stacy unwittingly sees this and even finds out Perry's agent secret.