I would talk to him and tell him that continously being engaged in mobile will get him sight from which he would have to wear glasses. I would also tell him by getting engaged in mobile he would not get anything. He is wasting time and avoiding studies due to which he is indirectly spoiling his career. I would tell him to come out and play so that he gets physical activity also. I will tell him he can play but not for more than 10-20 minutes.