Why do you think Holden cried after Phoebe gave him the money?

Holden isn't used to kindness. His whole world is built around pessimistic negativity about human nature. The one person he considers pure and good extends further kindness to Holden. This makes him cry. Holden's gift of the hunting hat to Phoebe is a significant event, for it is one of Holden's few meaningful possessions. He gives her the hunting hat as a sign that he may never see Phoebe again, whether because he has run away to Colorado or because of impending tragedy.