https://support.signal.org/hc/en-us/articles/360007319011-Ed...

https://signal.org/blog/contact-discovery/

But if you don't believe anonymity is an important component for security, you probably think hashes uploaded and deleted are perfectly secure, too, so we're probably not going to come to any agreement here.

Personally, I do wish they'd decouple from phone numbers and allow users an option not to transmit hashes for their entire contact list. I don't think these are unreasonable features for a messenger that's supposed to be designed for privacy and activism.