Depends on your climate. As a general rule you should never store any sensitive equipment in a car that is parked in the sun. (On the cold side, yes, not great for any battery.)
Another possible topic: Phone in sub-zero temperatures
My car will complain at me if I run things with the electrics on without the engine running for more than X minutes (presumably on the expectation that it will run the car’s battery flat).
In addition it offers two USB ports, one that is only powered when the electrics are on (wouldn’t be the case in a car that is abandoned overnight) and one that is powered directly from the battery and hence always on (until the car’s battery goes flat).
So clearly it will depend on make and model of car.
I would have thought … just shut the phone down overnight.