Which of those links actually say that your phone number is private from Signal? If anything, this passage makes it sound like it's the reverse, because they specifically call out usernames not being stored in plaintext, but not phone numbers.

>We have also worked to ensure that keeping your phone number private from the people you speak with doesn’t necessitate giving more personal information to Signal. Your username is not stored in plaintext, meaning that Signal cannot easily see or produce the usernames of given accounts.