One of the main messages in The Catcher in the Rye is that humans desperately need authentic connections with others who care about them.
Holden Caulfield has become an iconic representation of the angst-ridden and moody teen. He swears, drinks, and demonstrates an overall pessimistic view of the world. Expelled from multiple schools, Holden feels that his situation is fairly hopeless and roams around New York because he can't bear to tell his parents the truth about his most recent failure.
Yet in some ways, Holden's inner turmoil is perplexing. After all, his parents have enough money to send him to expensive boarding schools. He has two parents who are still together and who seemingly go to great lengths to help him. His older brother is a screenwriter, and he adores his younger sister.
Holden's tragedy is seemingly rooted in the loss of his younger brother, who died several years prior. This loss deeply affected Holden, who used his fist to smash out the windows in their garage in the immediate grief that followed Allie's death.
Following this loss, Holden is left fairly isolated and unable to make lasting connections. He doesn't want to trouble his mother too much; he worries about her health following the loss of Allie. His father is represented as a fairly dismissive parent, seemingly using boarding schools to house his troubled son so that he doesn't have to intervene much himself.
Holden has a "friend" who asks him to write an essay for him and then harshly judges the final product. Desperate for conversation and connection, he enlists the services of a prostitute without ever really intending to have sex with her; this ends with Holden getting punched in the gut by her pimp. Holden's need for connection is evident by his generosity toward the nuns he meets while eating breakfast; he offers them more money than he initially offered the prostitute.
Holden desperately attempts to connect with various people, from a former teacher to a potential love interest. Ultimately, he finds empathy and true acceptance from Phoebe, who grabs a suitcase and offers to run away with Holden. Through this connection, Holden begins talking about the real source of all his pain—Allie.
The way Phoebe supports Holden demonstrates an authentic compassion for his conflict and pain. She helps Holden feel heard and seen, which is arguably what he has been searching for all along.