Try to see things from the perspective of a child. Or if that's too far away, a teenager. Didn't it always feel unfair to you that the adults could do all these things, were free to decide what they do and especially what they didn't have to do? Althewhile you were literally forced to go to school and could decide almost nothing? Especially later on, when you felt like an adult but just weren't on paper (not even talking too much about myself here, I had more freedom than most).
And that wouldn't have been completely unjustified. The way society forces teenagers, young adults even, into these states where they get no freedom about their lives is not something that's necessary natural, not necessary the right thing to do. I mean, for something easier, look at the utter harmless jokes of PC games that were censored back then for non-adults (and effectively even for adults, depending where you lived). That really was unfair and ridiculous. Heck, one of the most influential games I played back then was Deus Ex, would be seen as completely harmless today, it was rated 18+. Crazy.
Being completely unjust with things like phone usage can't help with all of that. Do as I say, not as I do can't be a great guideline for how to handle these things.