More generally, the school has a big focus on anti-bullying and the kids generally seem much nicer and more together than my memories of middle school.
That's an interesting concept! Here in Ontario, Canada... it's my understanding that teachers have limited ability to take phones away from students... but they don't really want to because it becomes a liability issue. Some of these phones are worth $1000 and if the teacher misplaces it or another student swipes it, the teacher can be on the hook.
If the policy is that the student doesn't get the phone back at all, that changes things significantly.
That policy is commonly called stealing -- though it probably has a more specific label under law.
Schools traditionally have been implement civil-asset forfeiture for small stuff because people rarely kick up a fuss, and the schools can quietly hand things back when they do.
But if they start taking away people's smartphones there will be push-back.
https://www.uta.edu/news/releases/2013/09/jeong-bullying.php
Also, just because kids seem nicer and more together doesn't mean that they don't bully. Appearances can be deceiving. Though there are merits to confiscating phones from kids, we mustn't forget it also has drawbacks. Kids can't document bullying. Just because the phone is gone doesn't mean the bullying ends. It just means that the bullying can happen in secret and silence. We shouldn't forget that many child molestation by teachers and bullying by kids were brought to light because of smartphones. Smartphones are a tool. It can be both bad and good.