As you can now talk on Signal anonymously without sharing your phone number, there is a growing list of groups, for example here are some: Share your Signal Groups - Off Topic - Signal Community
There is also a group about Openstreetmap for users of Signal:
Global OpenStreetMap group.
This is not a channel of official OSM communication, refer to IRC and mailinglist instead. Only on-topic and mostly in English
List of OSM centric Signal accounts - OpenStreetMap Wiki for other groups.
I hear there’s an official community forum somewhere too 
Why would you assume you have to share your phone number (or even have one). Never been the case for IRC, mailing lists, here on discourse or even Discord.
Up until recently signal used phone numbers as the primary identifier. This has changed recently to allow usernames as identifier
Until this thread, I had never heard of Signal.
Have you heard about Edward Snowden then? He said he uses Signal every day.
By the way even Mark Zuckerberg uses Signal You might have heard about him.
It is popular in regions/countries of the world where there is a repressive regime, like Iran, China, Egypt, etc.
By the way, Signal works like Wikipedia or Openstreetmap, through donations. The users are NOT the product, like they are in Whatsapp etc (the user’s data is sold by the meta company, so Whatsapp doesn’t need donations nor direct advertisement in the app – but the data of the users is sold).