Phil is like the Ginger Rogers to Louie's Fred Astaire. He has to go through everything Louie does (being shot at, lost at sea for forty-six days, imprisoned in Japanese POW camps) but backwards and in heels.Okay, no heels, but he is the pilot of both the Super Man and the Green Hornet, and he feels a lot of guilt for being at the wheel (or whatever a plane has) when the Green Hornet goes down into the Pacific.
Phil has a less than illustrious beginning to his military career. He was small, short-legged, and his ROTC captain called him "the most unfit, lousy-looking soldier" (2.6.16) he had ever seen. But he quickly proves everyone wrong when he lands the Super Man after it is riddled with 594 bullet holes, and even though the Green Hornet makes a devastating splash down, he survives, along with Louie and Mac.
On the raft, Phil is mostly incapacitated, having been injured in the crash. But he participates in Louie's quiz show antics to keep their minds active. Keeping mentally active probably keeps Phil alive. He experiences so much guilt, he almost feeds himself to sharks: "There were times when Phil seemed lost in trouble thoughts, and Louie guessed that he was reliving the crash, and perhaps holding himself responsible for the deaths of his men" (3.14.29). It's a heavy burden, to say the very least.
Phil's a deeply religious man, and he spends his time singing hymns over the ocean. Maybe Louie absorbs some of Phil's spirituality subconsciously. Phil also pines for his fiancée, Cecile "Cecy" Perry. For her part, Cecy has a fateful experience right out of movie: She goes to a fortune-teller when she learns of Phil's disappearance, where she's told that he will be found before Christmas—a prediction which turns out to be true. They're finally married when Phil returns home from the war.
When Louie and Phil finally wash ashore, they get captured by the Japanese and shuffled from POW camp to POW camp. We lose track of Phil when he isn't suffering the same indignities that Louie is at the hands of the Japanese.
Phil calls himself Allen once again after returning from the war, and seems content enough being "that guy who was with Louie during the war." There is an event in his honor shortly before he dies, finally granting him a deserved moment in the spotlight.