Mac mini Phone app cannot make outgoing calls

I've tried to set up the Phone app on my Mac Mini [Tahoe 26.1] and am puzzled by the results: I can accept incoming calls and talk, using the Mac Phone app [1.0].

However, when I try to call somebody with the Phone app, an error message appears: "iPhone calls not available. You iPhone must use the same iCloud and FaceTime account".

I think everything is properly set, yet I can't find a way to solve this. Any suggestions?

Thanks,

Bob