Turn them off when you’re at rehearsal.  All the way off.

If you are expecting an important call that you must deal with during the rehearsal, put your phone on vibrate and give it to someone to hold, asking them to let you know at the earliest break in proceedings that your phone rang.  Most calls can wait to be returned until that break.  Unless your wife is going into labor or something equally urgent, tell anyone who needs to call you during rehearsals to leave you a message and that you will return the call as quickly as you can.

Text messages are a great way for people to get in touch with you when it’s urgent, because it saves you listening to long voicemail messages about things that can wait until rehearsal is over.

I’ve worked with people who leave their ringer on, but do not acknowledge incoming calls when they are on stage.  It’s fine except for the fact that it keeps ringing, and that is very distracting for anyone who is trying to act.  So please be courteous.  Once upon a time, we only had landline phones, calls waited until rehearsals were over, and usually nothing calamitous happened.

You are, of course, welcome to check your messages at any breaks called by the director.