How to criticize students who play mobile phones in class without embarrassment?

When the teacher's words are very important, he must not hurt the student's self-esteem, which has a great influence on his future physical and mental development, so be humorous. When I saw a classmate playing mobile phone without class, I knocked on the blackboard and said, "Someone is going to fall asleep with his head down!" " People will pay attention to you, so look at him and let him understand! If it still doesn't work, talk to him after class or after school!