The passage on page 81 of The Catcher in the Rye, which opens chapter 12, is a good example of Holden's depression, which is a major theme throughout the book. While large sections of the book are dedicated to Holden complaining about virtually all of the people around him, he uses the word "lonesome" multiple times in this passage. Some readers could interpret this as Holden's self-isolation adding to his depressed and melancholy state.
What made it worse, it was so quiet and lonesome out, even though it was a Saturday night.
In this line, Holden admits to himself, perhaps unknowingly, that he is lonely. This chapter opens with him complaining about the horrible smell of the cab, only to add that being isolated and alone is making the situation worse.
Furthermore, after lamenting his inability to speak with Phoebe, he says that he started to have a conversation with the cab driver.
I kept wishing I could go home and shoot the bull for a while with old Phoebe. But finally, after I was riding for a while, the cab driver and I sort of struck up a conversation.
These lines indicate that Holden is in need of human connection after noting that his current situation is "lonesome." Holden knows he can't communicate with Phoebe at the moment, so talking to the cab driver becomes a suitable backup plan and a way to cope with the depression that he fails to recognize at this point in the story.