alt Hacker Newsfuck. keeping your phone number off accounts is an important security step as many attacks require that you have a phone number connected.
If it's ever been on there you cant trust that some long forgotten recovery pathway can't be convinced to use it to authenticate access to your account.
Bonus-rage if the exploitable "recovery" path relies on "Security Questions" you cannot change which are not-really-very-secret and which overlap with the same questions recorded (and leaked) by other companies.