Phoniness is a very important theme in this novel, and being "phony" is a term that is used by Holden to refer variously to a series of characteristics that he discovers in those around him: superficiality, shallowness, hypocrisy and pretension. For Holden, phoniness becomes some kind of catch-all term to describe what is wrong with the world around him, and therefore becomes his excuse to withdraw into his isolated shell and not to connect. In Chapter 22, Holden suggests that phoniness is an unavoidable condition of being an adult, as society is built in this way and even if somebody wanted to be good, they would never be able to separate their actions from other phony motives. Note what he says about lawyers:
And besides, even if you did go around saving guys' lives and all, how would you know if you did it because ou really wanted to save guys' lives, or because you did it because what you really wanted to do was to be a terrific lawyer, with everybody slapping you on the back and congratulating you in court when the goddam trial was over, the reporters and everybody, the way it is in the dirty movies? How would you know you weren't being a phony? The trouble is, you wouldn't.
Holden then uses the term "phony" to sum up what is wrong with the adult world, and the various phony characters that he meets share a level of superficiality, hypocisy and shallowness that he finds incredibly frustrating and hard to accept. However, he sees this as something of an essential condition of being an adult, as he argues it becomes impossible to not be phony as an adult.