I can only speak for what I've seen, and my state has banned phones during school.

Before the ban, students would just openly use devices during class. Teachers were essentially powerless to do anything. Kids would be openly playing games, watching videos, etc with practically no recourse.

Now with the state law actually forcing it, enforcement is mugh higher. If phones are caught out the administration takes the devices and requires a parent to come into the school to sign off and release the device.

Does some usage still happen? Sure. Is it far less than before and considerably less during actual classtime? Absolutely.

It's like you're arguing murder still happens even though it's illegal so what's the point of making it a crime.