How hot is “really hot”? If the phone’s temperature goes above a safe limit the phone shuts down and displays a message saying it needs to cool off. If this doesn’t happen then the phone hasn’t overheated. Charging the phone causes it to get warm; the faster the charge, the warmer it will get; that’s just physics (specifically the 2nd law of thermodynamics). If you are going to charge overnight and the warmth bothers you use a lower power charger, a 5 watt “cube”, 7.5 watt Qi wireless charger or 12 watt iPad charger. The speed doesn’t matter, because even a slow charge will have the phone fully charged by morning.