Flight Safe Mode
As part of the security and safety announcement that gets made each time you get onto a plane these days, there's invariably a bit which goes something like this ... "all electrical equipment should be switched off during taxiing, take off and landing and all devices with a flight safe mode should have this enabled now".
This makes sense; in the case of an emergency, the airline wants you concentrating on the emergency, not your laptop or your phone. It may also be the case that the phone may in some way interfere with the flight systems. Opinion on this is divided but the former seems a more realistic option than the latter.