I say something similar in the context of parenting, that a reasonable amount of boredom is good. I think it likely that being constantly entertained makes people more prone to seek constant stimulation.
This did not start with phones either. I am Gen X and it happened in my childhood with kids being dumped in front of TVs. One difference was a lot of adults resisted this and limited hours in front of a TV, whereas now a lot of adults are addicted to phones too.