There is a dimension that you aren't considering. While it might be benign if one person does something, it might be less fine if everyone does it. Others might not be so good about turning off ringers, etc. Others might just decide to play games or chat with friends. It is hard to let this happen and also assure that it isn't disruptive.
The reason for the policy, I suspect, is that the instructor wants you to focus on what is going on in the class - exclusively. Even ten seconds away can cause you to miss something important.
But, I also suggest not getting into a fight with your professor ("handling teacher"). It isn't a fight worth having if you are so likely to lose it. Generally such rules, which may seem unreasonable to you, are put in place for valid educational reasons. There are tradeoffs, of course, but they usually favor paying attention.
There are other ways to be an effective learner that don't require electronics. They have been used for millennia.
I have written about effective classroom learning strategies that require only index cards and a pen/pencil at CS Educators as well as in other answers on this site.