Iphone XS does not ring when someone calls

I sincerely hope the articles below assists you:

https://support.apple.com/guide/iphone/adjust-the-volume-iphb71f9b54d/ios

https://support.apple.com/en-us/HT203800

https://support.apple.com/en-us/HT203794

My sister faced the same problem on her XS and it was determined to be a hardware failure. If, after checking the suggestion by jasonflying it still does not work; make an appointment with the Genius Bar, authorized 3rd party repair, or your service provider.

For me it was about dust and dirt in the headphone jack which told my iPhone that my ear buds must be plugged it. I blew the hole out and carefully used a q-tip to "dust" it. Then after resetting my iPhone for good measure, everything was back to normal. You must be careful doing this, however, to make sure that you don't push any dirt further up the port. You do this at your own risk.