But smart phones serve a purpose in schools and guns don't. Some school work can be done on phones. They're a reasonable thing to have between classes or when you've finished an in class assignment early. When I was in university, I frequently used my phone for further research of what the prof was talking about. I also used it for the calendar and reminders, which were so critical to me with ADHD fueled forgetfulness.

They're sometimes useful for accessibility. eg, I'm hearing impaired and my phone is the remote control for my cochlear implant. If live transcribe was a thing when I was a student, it would have been a major help. I'm sure plenty of other medical devices are using phones for that, too (I'm pretty sure glucose gauges for diabetics do this these days).

What purpose would a gun in school serve? It wouldn't even save lives like the American conservatives claim, cause it'd be way more common for students to kill each other over disagreements than to stop a school shooter.