Phillip is the youngest and the wild child of the Foxman family. He loves partying, going crazy, and meeting good-looking ladies. As Judd says, he's also the only one in the family who ever "come[s] out and says anything" (7.44). What could be the downside?
Well, as Judd puts it, "[Phillip] was alternatively coddled and ignored, which may have been a significant factor in his becoming such a terminally screwed-up adult" (1.38).
So, just how much of a screw-up is he?
You can say a lot of things about Phillip, but he sure loves to have a good time. He's the consummate hipster: he works at an underground record label, dresses like a rock star, and dates models. That's pretty different from his brothers, Paul the ex-jock and Judd the sad sack.
Of course, Phillip has his share of problems too. At the beginning of the novel, Judd and Wendy doubt that Phillip will even show up to the funeral. We never get a good idea of what problems haunt Phillip, but drugs and booze are likely culprits. Phillip, like many party kids, lost his way somewhere along of those crazy nights.
We think it comes down to this: as the spoiled younger brother, Phillip didn't get many boundaries or much guidance, with his parents seemingly exhausted from raising his three older siblings. Although he receives a lot of love from his family, he's never felt like he truly belonged.
At one point, he tellingly murmurs, "It would be so nice to believe in God" (50.9). With Philip, we get the sense that he's desperate for some sort of boundaries, something to believe in and look up to. We think that's why he unexpectedly decides that he doesn't want to sell his share in the store after all; he actually wants to work with his older, steadier brother Paul. Without a father or a father-figure in his life, Phillip is seeking any sort of structure that will help him grow up into a responsible adult.
Phillip's relationship with Tracy is his attempt to throw these issues aside and grow up. Judd may talk about how similar Tracy and Hillary are, but in our opinion the two women are pretty different. While Hillary is free-spirited (like Phillip), Tracy is tightly wound. In many ways, Phillip's choice of Tracy is more similar to his mom's choice of Mort.
In the end, however, Phillip learns that maturity is about more than just choosing a spouse. His decision to work with Paul at the store is a step in the right direction. The novel leaves it open as to whether there will be more positive steps in the future, but Phillip's future is as bright as it's been in a long time.