Behind the counter there are eight boxes on a shelf and each one has a number on the lid. When a phone has to stay, it goes in a box, and the number on the box is the number on your booking.
It sounds like a small thing. It is the reason nothing has gone missing here since we opened, and it is the reason the form will tell you the shelf is full rather than taking your phone and standing it on a desk behind a monitor.
Everything that comes out of the phone lives in the box with it: the old battery, the screws in a little bag, the case you left on. When you collect, the box is emptied onto the counter in front of you.