No not at the moment. Reason being is a phone number was necessary from the beginning when it was Text Secure and used SMS as a means to send e2ee messages. Using phone numbers as identifiers for your existing social graph was necessary for onboarding.

However, usernames are in the works and expected to be implemented in early 2024. Once that is complete a phone number will only be necessary for registration, and no one not even Signal will be able to associate a phone number with a username unless you want them to.

Retaining usernames for registration is a good idea because it prevents would be spammers from just creating a near infinite number of accounts.