iphone battery hot

Check the Battery Health on the phone.

Settings > Battery > Battery Health

if the capacity is less than 80%, the battery needs to be replaced at an Apple Store or Apple Service shop.

Make sure that you have Optimized Battery Charging turned on for the phone as well.

The support article you arrived here should provide you with a good explanation of what to expect temperature-wise with using your iPhone. What is "hot" to you is, of course, subjective, but it should never get that hot that you cannot comfortably hold the phone. That could be a sign of a pending battery failure. Bob Timmons has already provided you with how you can check your phone's battery health. Based on your answer, it doesn't sound like a failing battery. However, again, if you are still concerned, taking it to your local Apple Store or Apple Authorized Service Provider would be the next best logical step. Alternately, you can contact Apple Support directly to request mail-in service. To contact them, simply select the "Get Support" link in the upper right-hand side of this forum's web page.