There could be several reasons for the overheating of the Android phone:
If you phone are overused, then it can cause overheating. It could be that you are connected with Bluetooth speaker, Wi-fi network or left the mobile data ON all the time. So, it is recommended that you must switch of Bluetooth, Wi-Fi, Mobile data off when not required.
It is also possible that using your phone camera for longer period of time can also cause overheating. Some android phone displays the warning message when they get overheated. Beside this, if your phone brightness is high, then you must manually reduce to the lowest point where you can able to use your phone.
Another cause is virus. Don’t ignore this part, if your phone got infected with virus or malware, then it can create excessive heat. So, your Android device must have one anti-virus app to detect and remove virus from your phone.
It is also possible that your phone heat is not vented out due mobile cover or case. Almost every mobile case is made up of plastic or have larger amount of plastic, if not plastic then it could be leather and these all keeps heat in and cold out. So, when you perform multitask or play heavy games, then it is recommended that you must remove mobile case or cover.
Another possible reason could be your battery and charger cable. If your phone is left for charged and when it is fully charged 100%, but still cable is not unplugged then it get overcharged that could lead to overheating problem. In such case, you must always unplug charger cable, once your phone gets fully charged.
So, these are some basic but very handy tips that you can follow to avoid your Android phone from overheating.