Using an iPhone in high temperatures can cause permanent damage to the device. It could also trigger several behavioral changes, including slowing down or stopping charging completely, a dim or black display, cellular devices that get into a low-power state, and decreasing signal strength.
Others include the flashlight getting temporarily disabled, and the performance deprecating with graphics-intensive apps or features.
It is crucial that users keep their devices cool in high temperatures, and Apple have a few tips for this: They should not leave their iPhones or iPads in the car all day and not leave them in direct sunlight for an extended period of time.
Users are advised not to use sophisticated features such as GPS tracking or in-car navigation, play graphics-intensive games or use augmented reality apps in the heat or direct sunlight.
Users can also remove the device from the case to reduce the temperature.
It is important to note that any device that uses a rechargeable battery is susceptible to permanent damage once it is exposed to high temperatures. Devices such as iPhone, iPad, Android smartphones, even flashlights and other gadgets are no exception.
The sources for this piece include an article in ZDNet.