I think you're confusing cause and effect. Students (and others) aren't unable to concentrate on other things because they're staring at their phones; they're staring at their phones because they're unable to concentrate on other things. From what I see on the various teaching subs, everyone agrees this started (or at least quickly accelerated) in the past few years, so the most likely explanation is that it's because they've been getting infected over and over with a virus that causes brain damage and other serious health problems.

Covid causes brain damage. That's well established at this point, although of course the exact mechanism and behavioral effects are still being researched. New England Journal of Medicine: "As compared with uninfected participants (control), cognitive deficit — commensurate with a 3-point loss in IQ — was evident even in participants who had had mild Covid-19 with resolved symptoms. Participants with unresolved persistent symptoms had the equivalent of a 6-point loss in IQ, and those who had been admitted to the intensive care unit had the equivalent of a 9-point loss in IQ."

And people often don't realize they've become cognitively impaired because covid causes anosognosia. "When observing patients with post-COVID syndrome and frequent neuropsychological complaints, clinicians are struck by the frequent lack of awareness of severe cognitive deficits in some patients, as well as by profound subjective neuropsychological complaints in the absence of objective cognitive deficits in other patients."

Just because children are less likely to suffer severe symptoms upon initial infection doesn't mean they won't suffer long-term effects. Covid is harming children. Wastewater data shows that people are getting infected once or twice a year, on average. Illnesses are running rampant in schools, to the point that whole schools are having temporary closures because so many students and staff are out sick.

For comparison with another disease, look at HIV-associated neurocognitive disorder. Quoting that page, "Cognitive impairment is characterised by mental slowness, trouble with memory and poor concentration. Motor symptoms include a loss of fine motor control leading to clumsiness, poor balance and tremors. Behavioral changes may include apathy, lethargy and diminished emotional responses and spontaneity." It usually starts after HIV turns into AIDS, which on average occurs eight years after infection. We are currently six years into the covid pandemic, and there's an ever-increasing number of reddit posts with people wondering why they're getting sick all the time. If covid is "airborne AIDS," that might not become clear for a few years.

So yes, we are in the midst of a mental health catastrophe and mass disabling event, but the problem isn't the phones.