My thoughts as a High School teacher: I have tried[1] to allow students to have their phones, teach them to use their phones responsibly, etc. It doesn’t work. They are banned in my class. I’m just a single teacher with basically no budget. I can’t compete with giant corporations that spend millions on design, UX, UI, etc. [1] Also, technically trying to teach kids to use their phones responsibly (or even generically…
You could try silently writing down which days you saw a student on their phone & which days you taught the specific subject material.
Then when students get it wrong on a test that you grade you can add a comment along the lines of "this was covered on day X when you were on your phone"
You would also then have a nice report for parent student meetings, and the parents can do the enforcing