On iPhone, open Settings, tap Phone, and your number appears at the top under My Number.
Apple keeps your number in a few places.
Android wording varies by manufacturer, so I've listed the common variations.
When every menu fails, there's a method that works on any phone ever made: call or text someone.
Finding your number is one thing; sometimes you want the opposite, to keep it private when you call someone.
Read the complete breakdown, fixes and what happens next.