This is a phone jail for an iPhone 16 Pro, with Apple standard silicon case.  (Or other phones that are smaller).  The door can be glued in place for maximum security.  Lock your kids' phone up when they lose privileges, or your own phone to keep you from mindless scrolling.  

I also added an NFC tag and made a quick Automation in the iOS shortcuts app to automatically change the wallpaper to the “jail cell” image when the phone is inserted.  

I had the best luck printing the door flat on its back, and the cell body vertically (with supports, though they might not be strictly necessary).