Since the novel is satire, Salinger's focus is more on the society as phony rather than the individual. Of course Holden is a phony, but it is only because he is a victim of the phony culture.
On the phony scale, though, Holden is pretty low: he is materialistic and obsessed with sex. But, he's tame compared to Stradlater, for instance. Here are the major phonies:
1. Glad-handing adults (headmaster)
2. Over-sexed teens (Stradlater)
3. Pretentious snobs (Luce)
4. Celebrity-obsessed girls (in Lavender room)
5. Materialistic artists (D.B.)
Now that he is given a choice as a young adult, Holden is deciding whether or not to drop out of the phony culture. He doesn't know if he is courageous enough to live as a non-phony for the rest of his life.
Holden fears being a hypocrite, or a phony. He wants to live a quiet life surrounded by books instead of people and money, but he's afraid that he'll be the "wrong kind of monk," a "stupid bastard."
Later, on his run-away journey in the city, Holden sees two nuns and their dilapidated suitcases. The nuns also are symbols of holiness, and their suitcases are symbols of modesty, humility, and anti-materialism. Holden likes the way they look and the way they "never [go] anywhere swanky for lunch." As such, nuns are some of the few non-phonies in the entire novel.
All this is echoed near the end of the novel when Holden gets advice from Mr. Antolini, an Italian and--like Mercutio and the nuns--likely a Catholic. He says Holden is “in for a terrible fall”:
"The mark of the immature man is that he wants to die nobly for a cause, while the mark of the mature man is that he wants to live humbly for one."
Was Mercutio a noble man? Are the nuns noble? Would Holden be noble if he becomes Catholic? Or joins a monastery? What is Holden's noble cause?
Holden could end up like Mercutio or the nuns. He could die for a noble cause, like Mercutio and James Castle, both of whom committed suicide. Or, he would live humbly for one, like the nuns.