Actually you may have been thinking of the place in Chapter 2 where Holden remembers leaving Elkton Hills while he is talking to Mr. Spencer.

One of the biggest reasons I left Elkton Hills was because I was surrounded by phonies. That's all. They were coming in the goddam window. 

Holden states that the headmaster at Elkton was ten times worse than the headmaster at Pencey, and gives some indications of what he means by his term "phonies." Evidently Holden thinks that a phony is a person who is always putting on an act and has become so proficient at it that he doesn't even realize he is doing it. This seems to bother Holden extremely. He states:

I can't stand that stuff. It drives me crazy.

Holden doesn't try to explain his feelings about the Elkton Hills phonies to Mr. Spencer. 

I didn't feel like going into the whole thing with him. He wouldn't have understood it anyway.

In Chapter 22, when Holden is talking to his little sister Phoebe, he tries to tell her why he has gotten kicked out of Pencey.

"A million reasons why. It was one of the worst schools I ever went to. It was full of phonies."

We learn in Chapters 22 and 23 that one of the teachers at Elkton Hills was none other than Mr. Antolini. Holden likes him and apparently doesn't consider him a phony until that night. Then he finds out that Mr. Antolini is perhaps a bigger phony than anyone else he had previously known. It dawns on Holden that Mr. Antolini is a homosexual who is attracted to young boys like himself. This suggests that the teacher may have been working at private schools because they gave him access to so many boys. It further suggests, at least to the reader, that Mr. Antolini, who now appears to be a part-time instructor at NYU, may have had to leave Elkton Hills for reasons far more serious than those that led to Holden's departure. It would be ironic that Mr. Antolini is chiding Holden for getting kicked out of Elkton Hills if Mr. Antolini had gotten kicked out himself.

Holden Caulfield, the protagonist of J.D. Salinger's The Catcher in the Rye, seems to be infatuated with the phonies of the world. He calls his schoolmates, actors in New York, and girls in a bar all phonies. Curious enough, Holden proves himself to be the greatest phony of all of the characters in Salinger's novel. 

Holden calls his schoolmates phonies in chapter two. During a conversation with Mr. Spenser, Holden goes on an internal rant, providing information for his audience regarding the phony nature of everyone at Elkton Hills (his school before Pencey Prep):  "One of the biggest reasons I left Elkton Hills was because I was surrounded by phonies." 

Later in chapter three, Holden talks about his schoolmates at Pencey Prep being phony. First he talks about Ossenburger: "I just see the big phony bastard shifting into first gear and asking Jesus to send him a few more stiffs." Later, he talks about Stradlater being a phony: "He was at least a pretty friendly guy, Stradlater. It was partly a phony kind of friendly, but at least he always said hello to Ackley and all." 

At one point, Holden even nonchalantly calls himself a phony: "I stopped on the way, though, and picked up Ackley's hand, and gave him a big, phony handshake." 

Overall, Holden simply thinks that the entire world is phony--himself included.