The problem isn't with devices or necessarily "screen time" but with the types of software on these devices. Social media is just 21st century TV -- that's why it's harmful. The platforms that are ad-driven and engineered to be addictive don't help us
connect in the same meaningful ways we get offline.
So as you might restrict your kids' time watching TV, parents should be aware of the amount of time kids spend on interactive TV. Phones are particularly demonized because their omnipresence encourages more consumption, but really they're just the physical manifestation of the individual problems starting inside the devices. (Aside: I'd really be curious to know the amount of time people spend passively consuming information on social media vs. creating / contributing.)
And as an industry I think it's important we find other business models. We build these apps for "stickiness" and "engagement" -- seemingly innocuous metrics that ultimately accumulate to form these larger societal issues.