At the risk of sounding clueless, how is it possible that Signal can’t say which account belongs to which phone number when the only concept of a username on Si

At the risk of sounding clueless, how is it possible that Signal can’t say which account belongs to which phone number when the only concept of a username on Signal is that of a verified phone number? When I initiate a conversation, am I not at that moment using a lookup which now people are saying does not exist!?