The registration teachers takes them in the morning so each class does it at the same time but with a different teacher. Same again at home time. Don't know where they are kept.
Because they are stored away, there is no temptation or blatant rule breaking. Plus no chance of them getting broken falling out of pockets, stolen or getting lost when changing for sports.
I would imagine the time taken up by schools dealing with phone issues would be significantly higher than 5 minutes at either end of the day. I would rather my childs school focus on teaching rather than dealing with students who need their phones every 5 minutes.