Matrix still has 3pids, including phone number and email. The most common client, Element, will by default ask you for your phone number when registering with

Matrix still has 3pids, including phone number and email. The most common client, Element, will by default ask you for your phone number when registering with the default matrix.org homeserver and the default vector.im identity server will associate your phone number with your matrix user. So by default (changing servers and/or opting out is easy and encouraged BTW), Matrix already works like you would prefer. This is BTW a main critique in the OP since it makes vector.im a PII and metadata aggregator.