Here's the thing, in general. Phone or no phone, the problem your mentioned is down to the teacher. I've had good teachers that are able to make a lesson entertaining and guess what. That actually works, people aren't bored to death and shit gets done.

To contrast, boring lessons, even without factoring in phones, nobody gives a shit for good reason. We just focus on something else, wetger that's a phone or something else isn't a factor. Its rather the lesson itself

To address the retaining info part. If somebody talked to you for about half an hour on some random thing you don't care about. How much do you think you would remember or focus on. Spoiler alert, probably not much

So the students are out of touch?