Tried getting the actual study but it is paywalled. I would like to understand what the researchers determined the mechanism of damage to be - was it the heating effect on the brain, since this is non-ionising radiation?
i think they could be making assumptions and its actually more related to something else.
for example, when kids play with toys they have to remember where they put it and how it works/looks and joins in with your other toys etc.
on a smartphone its right there on the screen, its use is designed to be effortless & convenient. minimal effort required to accomplish something.