As a concept that appears in every chapter of the novel, the motif of "phoniness" is central to Holden Caulfield's worldview and character development. Holden frequently criticizes the world around him, particularly adults, for being universally superficial and disappointingly insincere. He uses the term "phony" to describe everything he perceives as fake or dishonest, which—at the beginning of the novel—he considers most things to be. However, as he grows, he struggles to come to grips with the failure of the real world to be just and truthful.
Holden sees “selling out” as a marker of being “phony,” including participating in careers that he sees as fake and superficial. For example, he criticizes his older brother D.B. for working in Hollywood, dismissing him as a sellout: “Now he’s out in Hollywood, D.B., being a prostitute.” Holden believes that D.B. has compromised his integrity for money and fame, and so he dismisses him using his favorite criticism. He also sees his fellow students at Pencey and most of the girls and women in his life as embodying the insincerity he loathes, as they say one thing and do another. The only people he thinks aren’t “phony” are children like Phoebe, whom he sees as still having the capacity to dream and to wonder.
However, Holden's obsession with phoniness is deeply hypocritical, as he almost always fails to convey or recognize his own “phony” behavior. Throughout The Catcher in the Rye, he does things that contradict his claims to detest fakeness. This is clearest in his tendency to lie, making up everything from a fake surgery to get out of sex to giving himself various pseudonyms. This tendency to fabricate stories shows that Holden doesn’t see his own insincerity as clearly as he could. He’s also an unreliable narrator, and as such is regularly “phony” to his own audience.
Holden's repetition of the term "phony" is one of the ways Salinger emphasizes that his protagonist is an adolescent. Holden is old enough to start noticing the flaws and failings of the adults around him, and he's also old enough to form an opinion about whether or not they are behaving according to certain standards. However, he’s not mature enough to be productively inward-looking and recognize his own shortcomings. His black-and-white thinking about phoniness at the beginning of this novel reflects this immaturity. Part of Holden’s narrative of growth is the realization that phoniness is not an absolute state. People can be varying degrees of "phony."