Until the Rosh HaYeshiva states that bochurim cannot go out for coffee breaks during seder, there is no reason why they cannot utilize the coffee break to check their phone that is in their coat pocket also. And that should be enough to assuage their mothers’ worries.
The Rosh HaYeshiva does not need my haskomo, but I have seen personally how distruptive it is (for ones’ self) to have a cell phone within reach while learning. And an entire Beis Medrash full of bochurim with cell phones magnifies the problem (so that it is constantly noticable how much battala it causes).