my iphone xs max temperature rises

Then it is probably normal. Do you have a case on the iPhone? If so, try taking it off and see if the phone heats up when doing the things you speak about, especially the web page. If you are using cellular data with a weaker signal and loading medium to large websites, with a great deal of images, etc., then it is probable the phone will heat as well.

If you are still concerned, then make a Genius Bar appointment at the nearest Apple Store to have the phone examined by Apple. It would help if you can duplicate the behavior when you go to see them.

What are you doing when you are connected to cellular data? How strong is the signal for cellular? The area you describe is where the processor is located, and if the phone has a weak signal and you are using the internet for video, games, anything that requires a great deal of processing power and graphics, the phone will get warm. Hot, is subjective, and everyone can describe that differently. Does the phone automatically turn off and display an overheated message?

I'm sorry you are having a problem, but I don't believe there is a problem with the phone. It just happens to be what happens when you are dealing with lower signal and extra work on the phone. With a computer, there is a fan to help cool it, but with the iPhone, the case acts as the heat sync to dissipate the heat. Try using wi-fi as often as you can, and limit the amount of time you use the phone once it starts to appear to be hotter than normal. Good luck, and I understand your plight. Someday.

You're welcome.