Sometimes the phone is warm, I wouldn't even say hot. Could be because I bought lower wattage wireless chargers - I don't need it to charge fast, I just need it to top up the battery.

The only time my phone has given me a message about heat was, indeed, in a phone holder in the car, but it wasn't even charging. We are experiencing a heat wave in Australia right now though, and the car had been sitting in the sun in a car park for an hour.