You're supposing that there existed a virtuous past in which parents taught their children respect and that if we returned to that past, there would be no need to ban smartphones in the classroom, and you believe that even though this virtuous past had no smartphones.
that’s why the pendulum has swung as far as it, in the direction it has!
That doesn’t make it the right call, necessarily legal in every jurisdiction, or even moral (in certain edge cases).
Calling back to my earlier comment: handing your kid an iPad for all of their free time is easy, too!