Must often expresses a strong obligation judged by the speaker; have to often expresses an external requirement, though they overlap. Should gives advice. Must not means prohibition; do not have to means no necessity. Past obligation usually uses had to. Do not turn advice into a compulsory rule when reporting a family agreement.
Topic preview: May I ask how everyone in our family uses a phone in the evening? I use mine for homework as well as entertainment, while Grandmother uses hers to see family photos. Those different uses matter when we discuss limits. Our preferences differ, but we all want attention when speaking. Could we agree on a phone-free meal and review the rule after a week? We should explain an urgent exception before assuming that someone has broken the agreement. Adults should follow the shared rule too. I would ask each person what feels difficult and suggest a practical compromise rather than describe one generation as careless or old-fashioned. Listening to an explanation does not mean agreeing with every opinion. It gives us a fairer basis for deciding what to do together.
Follow-up: What if homework needs a phone?
Response: Explain the task and agree on a time; distinguish study from entertainment instead of banning both without discussion.