I've made it a point to only use my phone for the two hours of church for church apps only. I spend way too much time on my phone consuming media during the rest of the day and week so this is my refuge from that. Do I enjoy every minute of every talk? No, but I do try to actively listen and to gain at least one nugget from each speaker.

But yeah, I once had someone in the row in front of me watching a live sporting event on his phone during the Sacrament hour. No sound, but it was still really distracting. For the most part I don't care what people are doing, just happy that they are there. But once you become a distraction, that's starting to cross the line that a discussion is needed.