The latest beta release of the Signal desktop app has picked up a feature the mobile app has had now for years: video and voice calling. Unfortunately, they're one-on-one for now, but it's already live on macOS, Windows, and Linux.
As per the Signal yooj, video and voice calls are end-to-end encrypted. While the announcement only explicitly mentions calls between desktop platforms, support documentation doesn't mention any restrictions, so I assume it should work for calling between phone and desktop.
Interested parties can follow the instructions here for their desktop platform to jump into the beta if they're itching to try it out. There's no specific timeline yet on when group calls might work, but we have to assume that's planned.