I dunno ... I've been around decades before smartphones and there was plenty of loneliness then, or times when people preferred solitude. I think smartphones have given connection to a lot of people who were otherwise alienated. Granted, I think using your phone when in someone's company is rude, and it's rather sad when people use it to neglect those closest to them. As @LiterateHiker pointed out, it signals "You're not important."

"You're not important" is the message you send by looking at your phone while meeting.

It's a rude, disrespectful dismissal.

I leave my phone behind on hikes, in meetings, on dates and at the gym.

I was antisocial before smartphones

But of course they are not ignoring people on the whole, they are just communicating with someone else, who is not in the photo.