Why is my charger getting hot when it’s not plugged into my iPhone?

Thanks. Regardless of, whether or not, it is a genuine Apple power adapter, it getting "hot" is not a good sign. It should never get "too hot to touch." If you feel that it is, even when it is not supplying power to your iPhone, it may be possible it is defective.

At this point, I suggest that you stop using it and take it to your local Apple Store or Apple Authorized Service Provider to have them take a look and provide you with your options.

Is this an Apple power adapter? If so, did you purchase it directly from Apple or an Apple Authorized Reseller?