You just need to keep on saying the same thing and be consistent. It’s the only thing I’ve found over the years that has any effect. Well since we had the things we had at our disposal as cadets removed. There are no real sanctions you can impose that have any real meaning anymore. I would stop them flying/gliding, but pointless now.
Do NCO courses cover how to handle low level disruption?
Something I throw at our NCOs if they complain about being fed up with newer/younger cadets is, what were you like? I can point out their failings when they were cadets, this gives them some perspective and appreciation of the situation.
As for phones in a box in the office until the end of the night and staff leave their phones in the office when doing instructing etc. Nothing worse the some banal ringtone/buzz/ping during a lesson, summoning them to obey.