Hey, Firstly, you want to make sure that when he says he likes you, he means in a romantic sort of way. He could just like you, as a friend. You may want to make sure of that before anything else. no use in assuming feelings that aren't there.
Now if you do know that he likes you in a romantic way, then it could be he is not very good at expressing his emotions, or it could be that he is very shy. If this is the case, expect to be doing most of the initiating. Most guys are afraid of rejection, so make sure he knows how much you truly care about him. If he thinks that he is going to get hurt, he will put up a defensive shield. So you need to work out how to get through it.
Do you ever talking to him outside of texting him? Maybe you need to if you don't. You need to seriously tell him that you really like him and you really don't understand why he doesn't answer the phone when you call. You just need to let him how you feel because like I said before chances are he may not feel the same way and you are thinking he does. Its really better to find all this out now then to get hurt later on down the road.
I would do this in person if it is at all possible. If not text him and tell him you need to have a serious conversation and tell him to please answer the phone.
Good luck.
-Lilla