Hi there lxilio2,
Thanks for stopping by the Apple Support Communities.
While capable of performing a variety of functions connected to cellular data, in order for the Apple Watch Ultra to make and receive calls without its paired iPhone, it must be connected to a Wi-Fi network, per the information in Use Apple Watch Ultra without its paired iPhone - Apple Support. If your husband's watch is not connected to Wi-Fi when the iPhone is off, it is expected behavior that it will not receive calls, even if connected to cellular data.
When he does make or receive calls on the watch, both parties should be able to hear without issue. If he has not already, we suggest troubleshooting this by first restarting the watch, then making sure it has the latest watchOS software installed:
- Restart Apple Watch - Apple Support
- Update your Apple Watch - Apple Support
These will isolate the issue a bit for us, and may resolve it completely.
Don't hesitate to respond back if you still need some help.
Best!