Voicemail on a Stand alone apple watch

I got my daughter an Apple watch and set it up under my phone under family setup. She does not have a phone. The watch has its own number and is not linked to my number. It works great but I can't figure out how to set up her voicemail. We use Verizon. When I select "Call Voicemail" from her watch I get a "Call can not be completed" message.

More info on the family setup.

https://www.apple.com/newsroom/2020/09/apple-extends-the-apple-watch-experience-to-the-entire-family/