Well, you can quickly search up some information. I don't remember what it was, but I remember that once in middle school teacher said something I wasn't quite sure about, but also I wouldn't ask if I wasn't more sure. So I looked it up, seeing that I was right, I asked if it rather wasn't meant to be that other thing, he checked too and indeed he was wrong.
Also, my mind often wanders off. And it may happen that I suddenly can't remember something. Could just be some word I could look up on my phone in less than a minute. Option B: Keep thinking about it till the rest of the class. I can't stop thinking about that until I either remember or find it.
Next, spine. I am currently in high school. Phones are allowed here. Any time. So, I utilized my scanner and digitized one 500 or so page book I couldn't find on the internet, and then used it as PDF instead of a physical book. It is less likely that I would forget my phone. I wish schools would have options for e-ink tablets instead of having to carry many heavy physical books. That used to be problem mostly in elementary school and middle school. Same goes for note taking.
Obviously, the last example can be easily solved by modernization.
Fast talking teachers. I can't write that fast. I mean, I can, but then I can't decipher my handwriting, which is already hard anyway. Voice recorder is a quick solution. Obviously, it is easier to look through notes than audio, but IT IS NOT MEANT TO BE A REPLACEMENT FOR NOTES, just a help.
But do take that with a pinch of salt. Especially in elementary school, I used to be one of those weird kids who greatly preferred being liked by the teacher over having friends. So even though I had a phone at the time, I never used it during classes because teachers disliked it.
But at least during breaks it should be allowed. Otherwise kids will find much more dangerous ways to entertain themselves.