At the individual level, yeah, there's not much to be done, but at the policy level, you can make massive improvements. The implementation of congestion charging in London had huge effects on air pollution. Conversely, adding highways to rip through the middle of old residential neighborhoods has clear detrimental effects on the nearby population. You can look at a map of childhood asthma rates in the Bronx in New York City for a really clear example of that; it significantly spikes in the areas near highways
(and of course, it's not a coincidence that highways tend to run through minority neighborhoods, so that's a factor as well)
Who is 'they'?
You're acting like there exists some single high council of concerned people who have unilaterally decided to pin all childhood woes on the phones, when this is a single article primarily about a particular group of UK parents who've focused on this issue and who presumably were never in contact with this American psychologist.
How do you know that these parents haven't also considered helicopter parenting and free play? Do you know them?