At that moment in that class, in order to protect other students' right to learn, I would ask that student using cellphone in class to give me his or her cellphone without hesitation directly, and continue my teaching first.
After the class dismissed, I would tell the student why he or she should follow the school rules. After graduation, you will start to work. For example, if you are lucky to be a flight attendant, you have to wear the uniform the company gives you and follow the firm's rules. Otherwise, maybe you can be fired or get lower payment. Therefore, in the school, you need not only to train yourself to be proficient in some specific professional subjects but also to cultivate your own personalities in order to be adapt to the work surroundings.