A friend of mine leaves the room to answer his phone. Why?

A friend of mine has left the room to speak to his phone twice. The first time we were hanging out with another friend and he answered the phone in the bathroom. I thought it was because there was noise in the room. After that he said he had to leave early to go to his house because his parents called and asked him to do something. The second time we were buying coffee and he left the store to talk to his phone. I am not tactless. I don’t know why he is doing this. Why could he do that? Have you done something like that in the past? Why?