[Forbo]

Does the design of Signal's applications or server infrastructure change because of the jurisdiction? Does the information they gather or store change?

[afiori]

With signal can you join public/private channels without disclosing your phone number?

The last time I checked (a few years back) I only saw private groups and no way to hide phone numbers.

If that is still the case then there are less reason to have a warrant for you phone number as it is easier to access.