Just the other day we had over 35C in my area (and my house insides too) and I observed that my phone had not charged much when I had put it on the charger (I know how fast it usually charges).
A bit of investigation revealed that the internal temperature (reported by an App that reads the temperature off the sensors inside the phone) showed that it was very close to 50C inside the phone, so I whacked it onto a "cold pack" until I could come up with a better solution.
This wasn't an ideal solution as while it chilled the phone it took it too cold and moisture condensed on the phone (known to technically apt as a "bad idea") and so I sought a proper solution at my earliest convenience. Indeed I expect that as battery damage occurs when temps are over 50C and would logically block or seriously slow charging (if you're an American reading this and don't know what 50C means then I expect the rest is technically over your head too, so don't worry).
From battery university:
Solution: get rid of heat
This is a heat sink.its made out of aluminium to enable it to rapidly conduct heat (from the source) and disappate it via the fins (which being black also allow for good radiation too).
So with my phone sat on this it was only a few degrees above "ambient" air temp.
which is great.
Somehow it happens that I didn't blog about my "home made phone stand" (from old wood) which I also made a few of for office colleagues:
I sit it like this when not charging:
but as the charging port is on the side, I turn it sideways (notifications harder to read that way as orientation sensor does not do everything everywhere) when charging. As it happens my "home made stand" also works to allow heat dissipation through the screen in this orientation..
I've always disliked phone covers (which will act to also trap in the heat) and so this only works well because the phone is in good thermal contact (it has an aluminium back even) with the heat sink.
Sorta looks funky too dunnit.