Hey there, BlueEyedDevil0716,
Thanks for stopping by the Apple Support Communities to get help with your husband's iPhone XS Max. After reading your post, we understand that he is able to make outgoing calls, but cannot receive incoming calls. You've come to the right place for assistance!
It looks like you have done some troubleshooting already, which is great. We would recommend going through the Apple Support article If you can't make or receive calls on your iPhone - Apple Support and performing any troubleshooting suggested there that you have not done.
If you still need help after going through the article, contact Verizon to ensure there is nothing on their end (either related to the network, or his phone number/account specifically) that may be preventing the incoming calls: Contact Us | Customer Service Phone Number & Chat | Verizon.
Should the issue still be unresolved after that, you will need to get in touch with Apple Support directly. You can do that here: Get Support.
Best!