His family is not pretending to live, they are not phony, what is phony is Holden's refusal to grow up. You can't stop the process. It is phony of Holden to pretend to remain a child, when he knows that, he is maturing into a young adult.
It is phony of Holden to say that he really cares about Jane Gallagher, yet he never calls her. Holden is a very depressed person, he is stuck in a grief cycle over his brother's death, refuses to accept responsibility and accuses everyone around him who lives their life of being a phony.*
*Holden has good memories about visiting the museum when he was younger. The thing