During every school period I can remember, and during long gone eras recounted by people much older than I, it is impossible to imagine a class without disruptive students (although not wanting to pay attention and looking at your phone does not seem particularly disruptive) and teachers have dealt with it. There was never a need for cops unless there was actually something criminal happening.
This insane reaction to kids being kids is just another manifestation of the desire to control on the part of those who hold some modicum of power. The school shootings, while abhorrent, do not justify putting thugs in charge (the Stones concert at Altamont should have taught everyone that lesson).
Teachers need to be better trained to deal with de-escalation (especially when the students are just being their normal pain-in-the-ass selves) and the school administration should be actively involved in helping the teachers to deal with classroom issues.
Calling in a cop with a history of excessive force drives home the point that we have created a generation (or two) of wusses and dullards.

"The liberals can understand everything but people who don't understand them."
Lenny Bruce

"The cleverest of all, in my opinion, is the man who calls himself a fool at least once a month."