That’s the same guy who would go to a worship service and yell “FREEBIRD!” 
My wife and I saw Pat Benatar and Neil Giraldo at our local community college a couple weeks ago - 600 seat venue. No opening act. There were strict rules: no photography or video recording - under penalty of ejection from the show. As a result, people were pretty well behaved WRT the smart phone thing. We saw one person near the stage take some pics but otherwise no drama there. The show was pretty loud and entertaining, so we did not notice a lot of talking or side conversations - that would have been difficult to do anyway. Some were dancing on the sides.
It’s been a while since we saw Pat - lots of grey hairs (or no-hairs) in the audience. Even she has grey, and is a grandmother. Man, we’re getting old.
I don’t attend a lot of concerts but I always thought the onus was on the musicians to keep the crowds attention. If the crowd isn’t paying enough attention shouldn’t the folks on stage be the ones to blame?
That’s fine. But if you decide to take your seat DURING the opening act, would you wait until between songs, and try to take your seat somewhat quickly and quietly?
Maybe so, but it isn’t the fault of the musicians that the entitled audience members choose to disrupt the enjoyment of the people that are listening. If they aren’t listening they can still simply shut up, or leave.
I’ve been asked to stop talking at a relatively quiet concert a couple of decades ago. There was no seating, so we moved away from that idiot and continued our conversation. It is possible to converse and listen to music, and we were discussing the show we were watching, anyway.
Most other concerts that I’ve attended or performed at were loud enough that your ass was going to have to be outside to talk, though. Low attendance for the opening acts is almost a given and has been as long as I’ve been around. You’ve got to be something special to draw as much as the band you’re opening for.
Phones are the only thing that I’ve noticed changing. And the only real change is just about everyone has them. Folks have been taking pics and recording shows as long as the tech has been available. As a performer, they’re kind of great. Folks record/post your show and promote you. You yourself get a lot of recordings where you can see/hear what worked and what didn’t. From an audience members’ point of view, it’s kind of a pain for everyone who’s not filming.
This is the exact opposite of my experience. Many of my favorite bands were unknown (to me) openers for other bands I saw. I always try to make it to see the opener, and I’ve never been disappointed.
As for talking and phone use, I figure, they paid, let them waste their money if they want. Most bands are playing loud enough to drown out bar talk. People who yell out requests between songs are annoying as hell though. And people shouting during the quiet parts or worse, when the whole show is a low-key, solo acoustic affair and people can’t keep their mouths shut. Those guys suck. This is not a new phenomenon though.
Every picture or video I’ve ever taken at a concert has been essentially worthless, so I just keep my phone in my pocket now. If I want to see the stage again afterwards, some music journalist has taken much better pictures than me and posted it online as soon as the show is over, so I’ll just google it. But other people want to waste their money watching the show through a tiny, pixelated peephole, that’s none of my business.
I don’t go to many concerts at all, so I can’t recall if I’ve ever actually shown up midway through an opener’s set, rather than before they start or after they finish. I imagine that I would not bother to wait until in between songs, but I wouldn’t be obnoxious about it.