We have a small team, and have discovered that ONLY the phone number owner can see Voicemails left to a Shared Number. Speaking to Welma and Tanu, we tried various settings but there does not appear to be a way to let Team Members see Voicemails for the numbers they are members of in the mobile apps.
Instead, we have emails being sent with the VMs. This work around gets us out of trouble, but the in-app voicemail tab should be able to be used by Team Members as well as the Number Owner.