Here are some things to do if your phone overheats and shuts down:

1. Check to see if the phone is in a well ventilated area.
2. Clean the vents of your phone to make sure air is able to flow freely.
3. Disable certain app, such as gaming apps, that often cause overheating.
4. Make sure your phone isn't near any other objects that generate heat.
5. Allow your phone to cool down if it feels hot.
6. Replace the battery if it starts to show signs of wear.