A "neat" thing is that this exact same behavior is present in adults. Numerous studies have demonstrated a negative impact on focus (and other factors) when a person's phone is in their vicinity, even if it's completely inactive. I'd hypothesize it's our bodies becoming somewhat acclimated to the little micro-dopamine bursts you're going to get each time you get a bzzt, brrt, beep, or other sort of "engagement" (read: addiction) optimized notifier letting you know that something has happened. Even just seeing your phone, your body just starts anticipating it, and waiting for its next hit - in the same way your mouth may begin to salivate when looking at a delicious plate of food.

I suspect we'll look back at this era we're living in, the same way we might look back at the 19th century. In the 19th century cocaine started showing up in just about everything. It was used in medicinal tonics, casual drinks like Coca Cola (cocaine + kola nut), and more. People would use it recreationally, employers would give it to their workers, inventors and others (among them, Thomas Edison) would use it to improve their productivity, and more. Given the dramatic side effects of cocaine, people certainly realized there was a problem - but inertia is one hell of a beast.