Those also hit around the same time. People doom scroll on desktops and laptops too.
Honestly just infinite scroll alone is shockingly addictive. Pair it with algorithms that sort content by measured engagement and your brain stem doesn’t stand a chance.
Social media algorithms also prioritize trash content because that’s what maximizes engagement. Think of it this way. One person walks by on the street and says “hi.” Another walks up and strips naked and smears themselves with peanut butter and starts clucking like a chicken and saluting Hitler. Which one of these maximizes engagement? Which will the algorithm perpetuate? This, IMO, explains the evolution of political discourse over the past 15 years and is why a troll is now President.
Smart phones are just a particularly good platform for these systems, but it’s the systems themselves that are toxic. They work on a desktop screen too. It’s just that laptops and desktops aren’t as portable and are not always with us in the same way, which limits the damage.