When I was sitting a few rows behind him at Book of Mormon (somewhere I wouldn't have expected to see him) I did wonder to myself if he had turned his phone off like the rest of us. He didn't check his messages then though thankfully.
Sorry to echo what's been said, but was very underwhelmed by this. While the music is nice, it is not a strong piece, the book is all over the place and the plot incoherent at times. I like to support new musicals, but this was very disappointing.
I've only ever done this once, at The Magistrate at the NT, but only because I had a shocking migraine and couldn't even see straight. I waited til the interval but don't include it on the list of things I've seen because I didn't really see it.. I'd never walk at the interval, I like to see things through. I'm the same with films.