1st, find out the rules and liability of phones from your school. You don't want to be breaking school rules.
I used to use this to keep confiscated phones in. It started with confiscating them for the period when I caught a kid with it; then, it became where I put them until lunch or my prep period to take them up to the office.
This year, I'm (hopefully) using this. Cell phones and going to the restroom got really out of control last year, including kids using "restroom" trips to deal and exchange drugs. So, going to the restroom is going to cost a student their cell phone for the rest of the period.
Get a lockbox to put your hormones in.