You can find the answer to this right at the beginning of Chapter 23. Holden has called Mr. Antolini from his parents house. He's there visiting Phoebe. He doesn't say so right out, but he seems to be calling to ask if he can stay at the Antolinis'.
The first thing Mr. Antolini asks him is if anything is wrong. He doesn't seem too worried when Holden says he has been kicked out of Pencey. Then Mr. Antolini tells Holden he can come over and stay if he needs to.
Of course, Holden will go over and stay at the Antolinis' in Chapter 24.
Mr Antolini responds to Holden's telephone call with worry. His first step was to ask Holden if he was ok and if he needed anything. When he hears Holden's problem he invited him to his house, and gave him a place to stay. In a way mr Antolini is like a father figure for Holden, a person who watched out for him and understood him.