In signal, You can turn off phone number visibility and make it so that you are only searchable by username or qr code. Yes, it’s centralized, but signal is a nonprofit project with generally good guiding ideals. I use matrix for some things and signal for everything else.

Can confirm. I worked as a contract program manager for Microsoft with O365, Azure Gloval Ecosystrm, and yes, the dreaded Windows team. I wakk out out my last two Microsoft jobs in the middle of a shift. I would do it again.