Ever watch The Wire? The school in that show is a very accurate depiction of what a... middling-bad inner city school is like. There are tons of ones worse than it (they may have shied away from one of that sort either because it didn't suit the story, or because they thought too many viewers would think they were exaggerating)

There are schools where the administrators are too busy dealing with violence to have time for much else.

Are you saying that from a perspective where the purpose of schools is to offer an education, or to keep kids locked up and be cheaper than daycare?

These sorts of schools already make kids pass through metal detectors on their way in so phones can just be confiscated at that point.