Adding to the mix, perhaps consider addressing agenda items first and putting non-agenda items brought up at the beginning of the meeting until last. A) you might answer the question during the meeting and B) It protects the meeting from sidetracking. After all, you came to address the agenda’s items.

Mislav- Perhaps try enforcing the rule in a slightly different manner. If you must answer your cell phone, do so, but you must leave the room and can’t come back in. Clearly, if the phone call is important enough, you can take it. If it isn’t, then you’re not likely to leave to answer it.

Good point to schedule Bio breaks. A few minutes to hit the bathroom, stretch, or get a cup of something is always appreciated. There’s no polite way to take a bathroom break as a junior employee…