Why sometimes I really want to talk to people, sometimes I don't want to talk, and I just sit there and play with my mobile phone without saying a word. I am introverted.

When you want to talk to someone, you often can't find the answer or don't understand it, and then you want to talk to someone;

When you don't want to talk to people, you often know the answer subconsciously, and it's useless to tell others, so you keep silent and digest it yourself, and you don't want to add negative energy to others or involve others.

Actually, I don't know what you want to ask, and I don't know what answer you want to find here. But you can try to talk to strangers online about what you want to say. But keep it private and be careful not to be cheated.