First the phone is warm up to 45 degrees C.
Hot is more than 50 degrees C.
(There is a hardware monitor in the Support app on the phone).
We also need to consider the environment:
When the phone is used in normal room temperature at 20 C, it can become 15 degrees warmer and still be comfortable to hold. Outdoors in the sun, it may be 35 C before use, so an extra 15 degrees heat becomes uncomfortable.
There is protection circuits in the phone to prevent damage, but the phone can be uncomfortable to hold before it triggers the temperature protection.
It in doubt please consult the place of purchase or a technician.