Given the caveat that such studies are often looking for particular outcomes and thus suspect, there are a pile of studies documenting benefits of reading, incl

Given the caveat that such studies are often looking for particular outcomes and thus suspect, there are a pile of studies documenting benefits of reading, including (for several of them exclusively) fiction. We either do not have, or have the opposite result, from studies on phone usage. Given that phones are now just general purpose internet-connected computers, I would expect them to have orders of magnitude more variability in outcomes based on actual individual usage, but it's not identically the same cultural panic that happened when mass market fiction entered the market. It should be noted however for those not aware, that if you give people decontextualized quotes describing the behaviour of readers when mass market books were introduced, they assume they are current and describing smartphone usage.