Phineas Porpoise a nerdy dolphin who is a Charles Darwin Middle School student and the leader of The Spiffies in My Gym Partner's a Monkey.
He is voiced by Phil LaMarr.
Phineas is a gray dolphin, who walks on his tail fin. He has black, poorly combed hair, and thick, black rimmed glasses. He wears a cream colored shirt, with pens in the pocket, and brown pants, which come down to one leg hole, due to him wearing it on his tail. Phineas speaks in a high-pitched nasally voice and occasionally snorts in between emotion-driven sentences. When around the other Spiffies, his snorting kicks in at the same time everyone else's does.
Phineas is a nerdy, wise cracking know-it-all, who sees himself as superior to students of an average academic level. He takes great pride in his intelligence and behaves in a condescending and rude manner toward those, he sees as "beneath" him. He expresses vast knowledge in both the field of academics and the world of cultural media, and does not keep it hidden. Being a nerd, of course, he has no friends, other than his fellow Spiffies, and is a major target for bullying due to his physical weakness and annoying personality. Despite his weak and pathetic nature, he still asserts dominance over the four other Spiffies, establishing himself as the head of the pack. Phineas comes equipped with strong leadership skills and responsibility, making him fit for the role of "King of the Spiffies".
In "Animal Testing", Adam was transferred to The Spiffies class, and right off the bat, Phineas was guns-a-blazing, lashing out at Adam not being as intelligent as the rest of the class. Adam then proved his genius, winning his respect, and became part of the school spelling bee. Adam soon backed out, being afraid of losing his old friends. Shortly afterwards, Jake got transferred to their class and went through the same process.
In "Law and Odor", Phineas and the other spiffies ran the school courtroom. There were not easy on Adam and Jake, still being mad at them for losing them the spelling bee. They sentenced them to community service, making them work as hall monitors for a week.
In "My Science Project", Phineas entered a robotic suit in the school science fair, but found Jake and his Robot Arm to be competition. This started a big fight between them both.
In "Guano in 60 Seconds", Phineas was one of the many students to move from the school to the trailer after Jake's recent accident.
In "I Got a New Aptitude", Phineas was briefly seen taking the career aptitude test with the other Spiffies in Mr. Blowhole's class.
In "Carny Crazy", Phineas went to the carnival with a robotic arm, which, when programmed, would be able to target any subject and hit them with perfect aim and impact. He used this on the carnival's ball toss, giving him an unfair advantage against Adam, who was trying to win the final Princess Ballerina snow globe toy.
In "Making the Grade", Phineas and the Spiffies were hiding out in the sewers, during the uprising of the students. Their cover was blown by Bull Sharkowski, but Adam helped them appear as fellow idiots, by taking off their glasses, so that they'd be aimlessly walking around, bumping into each other.
In "Pants in Space", Phineas readied Windsor for going into outer space, by giving him a bunch of space travel testing machines to work with.
In "The Spiffanos", Phineas led the other Spiffies like an Italian mob, and reeled Adam into the group. After Phineas lent him a pencil, he asked Adam for a favor, which was to steal Bull Sharkowski's lunchbox. This plan failed, but instead of Bull taking out his anger on Adam, he wanted for everything to come down to where it first started. So, he asked Adam to do him a favor, which was getting revenge on Phineas and The Spiffies.
- His first name being "Phineas" is a pun on him having fins.