Devices are checked in on the kitchen counter when they are not allowed to be in use. Complaints about not trusting him should be met with, "You are correct. I do not trust you. You demonstrated that you are not worthy of my trust by violating the rules. I am disappointed in you. As a result of your own behavior, you will now be treated as if you were younger than you are. We will try again in a few months and in the meantime, you may work to build up my trust again by 1) brushing your teeth; 2) completing your school work..."
Frankly, if you plan on ever getting him a cell phone that does more than call people, get him used to checking in his devices on the kitchen counter.