How much will it cost to replace a stolen iPhone if I have AppleCare?

If you did buy Apple Care with Loss and Theft coverage, and the stolen iPhone is the XR in your tag line, the deductible for it is $229 in the U.S. Prices vary by country.

See here (scroll down to the service fees and deductibles section): AppleCare+ for iPhone XS, iPhone XS Max, iPhone 8, and more - Official Apple Support

AppleCare does not cover theft or loss unless you explicitly purchased AppleCare with Theft and Loss protection.

Did you?

If not, it will cost the full retail price of a new phone. Contact your homeowners or renters insurance carrier. A portion of that might be covered.

If you did purchase that coverage, you can submit a claim here: https://support.apple.com/iphone/theft-loss-claims