After numerous times of seeing people be on their phones during movies, and not saying anything, I finally mustered up the courage to tell someone to stop. Luckily he was sitting right next to me so it was easy, though.
We were in the last showing of the night for Mission Impossible: Fallout (fantastic movie by the way) and the movie slowed down for a few minutes and he pulled it out to open a news app and read a few articles. If it were something like having to read a text from his kids or something then I would understand, but I had enough with this happening at least fifteen times with other people in other movies. I tapped his arm and said, “Hey dude, there are people behind you trying to watch, put it away.” He apologized and put it right away! It was surprisingly easy and I’m really glad I did it.