I completely agree. I do not think this is a millennial problem. I go to the theater a lot, and I'm in this age group as well, the one's I see using there phones are either younger 12-15 year old or older such as in the 40s or 50s.
I only see it maybe one movie in every 20 or 30 that I go to. It also depends on the movie that is showing, tend to see it more in comedies aimed at teens or those romance dramas.
If they really want to attract millennials, this is not the way to do it. My suggestion is offer a place social engagement before or after the movie. Look at some of the things Alamo drafthouse is doing with a bar attached to the theater plus good dine in theaters with good food that you'd find in a decent restaurant. There is even one not very far from there new expensive Leawood Headquarters in downtown Kansas City, I'm sure they they can find it, it use to be an AMC.