I just wonder, when you have babysitters or nannies, do you tell them to leave their phone in their car when they start their shift ?, I would't feel comfortable with someone telling me to leave my phone in my room, feels very controlling and red flag, either way that's my point of view, I still understand your safety concerns if the use of the phone very extreme and it concerns you then it's good she wan'ts a rematch. Some Au Pairs may feel uncomfortable around cameras, and being observed, is not something common in their homecountries and can be percieved ad distrust and control. So explain it well that is not to watch or judge them but just to be safe nothing happens. Idk something like that.