RingCentral had some really nice features; we used it for our business several years ago and I had considered using it as a virtual clearing house for my family to help keep our personal numbers private when signing up for things.
I had even ported a Google Voice number to RingCentral well before that process was streamlined.
Obsidian, but I’m not competent to comment regarding their privacy. You can air gap the install and have it on an isolated machine.
It’s hella customizable, and there is broad support specifically for using it with TTRPGs.