You are really complicated...
So let's call it "User ID".Or if you like "Kontalk ID".
In Play store we use:"Your phone number is your ID."
Ok, then what about
Your [link]hashed[/link] phone number is your Kontalk ID and publicly visible throughout the network.
Great. I think that's perfect and understandable for non tech users like me.
OK, finally, added and translated into german.