I feel like once you are in high school, kids should be responsible for their own devices and how they want to use it as long as it doesn't bother anyone else. If the kid wants to fail his classes to play on their phone let them.
The reason I have this view is because most of my classes allow our phones to be used in class, I personally find it easier to concentrate on my work when listening to music so I don't have to hear other people doing whatever. Plus, i'll go on my phone and text during most times in class since i'm usually ahead or work on my own. I don't know, might be somewhat of an unpopular opinion but that's my view on it.
Also a side note: My high school is very tech oriented, most of our classes require use of the interwebs, we got school issued MacBook Airs, so that's another reason we get to use our phones a lot.