Indeed, most of my education was without (smart) phones, and teachers rarely had my raw undivided attention. I were quite frequently working on more interesting stuff (hobbies, math, stories), daydreaming, etc. Students are humans, and they have preferences -- and that's an excellent sign (that creates differentiation, that makes students more cognitively flexible, more adaptive). My preferences don't align perfectly with the curriculum and I were free to explore as I wanted (without disturbing other students of course), as long as I did my duty of learning enough to pass the course. In the worst case I've always had the refuge of my mind.

To demand sole attention unconditionally and continuously is thought-police-alike.

That said, there are certainly perils with too much distraction and smartphone usage. I'm a firm believer in human instinct guiding toward positive usage of technology, but there are unquestionably failings in our instincts -- there have been for quite a while.

Television was a big one for me -- it's immensely more attractive than a book; but books can be much more gratifying and educational once you get started; it's just more work. Yet there was always a lot of value added by judicious usage of television -- documentaries, non-vacuous talk shows, good film, etc.

Online games too -- I've spent a good chunk of my childhood in front a PC playing an MMORPG. Seems like a waste of time (and some of it was), but I've experienced a world of politics, fierce competition, intense cooperation, trading and all sorts of economical endeavors, friendship, cruelty and kindness in the safety of my home, with people of diverse backgrounds and cultures; I've learned a English and became extremely proficient almost entirely through the game. It also ran the risk of getting me addicted and isolating me entirely from real life social interactions; that risk was averted (and I would certainly still have a dearth of social interaction due to family problems) -- mostly through my own good judgement but also from pleads of caution from my parents and siblings. I still remember events, lessons and friends from those days.

Surprise: we'll have to keep dealing with the ambivalence of technology.

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"The one solid fact is that the difficulties are due to an evolution that, while useful and constructive, is also dangerous. Can we produce the required adjustments with the necessary speed? The most hopeful answer is that the human species has been subjected to similar tests before and seems to have a congenital ability to come through, after varying amounts of trouble. To ask in advance for a complete recipe would be unreason­able. We can specify only the human qualities required: patience, flexibility, intelligence."

From 1955: Can we survive technology?

http://geosci.uchicago.edu/~kite/doc/von_Neumann_1955.pdf

"What kind of action does this situation call for? What-ever one feels inclined to do, one decisive trait must be considered: the very techniques that create the dangers and the instabilities are in themselves useful, or closely related to the useful. In fact, the more useful they could be, the more unstabilizing their effects can also be. It is not a particular perverse destructiveness of one particular invention that creates danger. Technological power, technological efficiency as such, is an ambivalent achievement. Its danger is intrinsic. "