If you have enough advanced notice many schools post the student handbook on the school website where you could review key policies like phone use. Asking the school staff when you check-in would be another option.
Your question should be a reminder to those in the classroom on a daily basis to include such information in their "sub folder". When it's used daily we often forget the person covering for us may not know.
When I was subbing I often let the classes know that I would be following the instructions left by their teacher, but may do some things differently because I am not their teacher. Sharing what your expectations are for the day/class can also be helpful. Do your best to avoid power struggles as this is what students will try to do especially with a sub. Remind them their choices have consequences. Those can be positive or negative. If they choose to work the consequence is in the form of a reward because the work is done or maybe less homework. If they choose to not work consequence is negative as the work still has to be done and a call to security or whatever the school policy is.
Whatever you do stand your ground. Let them know you won't be intimidated or pushed around by their poor choices or behavior. The expectation is that the plans left by the teacher are to be completed.
