iPhone x and 7 heating up to 90 degrees

This happens on my 7 and X seperate apple ID's as one is for business

When I put my iPhone against my skin specifically he top right corner it feels warm. I borrowed a thermometer from a friend and t was reading 88-91 when making phone calls and also doing daily things like reddit facebook and safari.

I’ve read some people say it’s normal and others not so I was hoping some people could let me know or actually check the temp of there phone after 30 minutes of moderate use? The phone call was only roughly 7-10 minutes and I can check with a thermometer and it will be 90 degrees, no case on it just holding it against my face when talking.

Is this hand heat? Is it normal?

Thanks!