There’s a bunch of topics covering this.
But, my iPhone 7+ gets quite hot too.
First of all, there’s nothing wrong. The back itself is designed to work as a heat sink.
There are basically four things you can do to avoid heating;
- Avoid charging while you’re using IF.
- Lower the screen brightness as much as possible.
- Make sure to have “Limit frame rate” ticked in the graphic settings for IF.
- If you have an extra back cover or smth, remove it. It stops the heat from escaping throughout the back of your device.
There’s really not much you can do otherwise. It happens when you use other performance demanding applications as well.