I had a laptop as a server for a really long time, and I also poked around using a phone for some server things (not as main server) and after some time it was unusable (the whole phone was suffering because wasn't prepared for a battery that fucked).
Anyway, my point is, maybe his phone has some mechanism similar to laptops to prevent this kind of thing, but in the end it's a phone. It's not the intended use for it.
Well, maybe, but could that not also be the chance thing I mentioned? That it greatly increases odds, but a 'great increase' of 1% per decade is still not more than a third of the cases or so. Or it's the bypass charging that a sibling comment mentioned indeed
Anyway, my point is, maybe his phone has some mechanism similar to laptops to prevent this kind of thing, but in the end it's a phone. It's not the intended use for it.