Public transports are really amazing with this respect. Many people are just absorbed by their phone not paying attention to anything around. Same happens in classrooms.
I have the chances to lecture to small groups of students. Phones are banned. I fully agree with what you said regarding focus, attention, etc. I witnessed the difference.
In short, we need to impose discipline to ourselves with our phones :)
RE: The joys of (mostly) switching off from social media