When the written word took over with the printing press, the same concern was levied. The amount of attention required to listen and memorize a story/poem is a lot more than just reading it.
The change with smart phones is just one of access/time spent on these things. There are people who are spending ~5 hours/day watching this content. There is a big difference between someone listening to 5 hours of a single poem, to reading 5 hours of a single book, to reading 5 hours of blog posts, to watching 5 hours of a youtube video, to watching 5 hours of random videos, to 5 hours of <10s videos.