How to check MTN phone number.
I will not bore you with unnecessary details.

To check your MTN phone number dial *663#, your phone number will pop up and get texted to you as well. Yeah, it's free!
How to check your GLO phone number
Unlike the MTN, To View your phone number on GLO is not straight forward but it still cost you nothing to do so. To view Glo phone number get a pen, book any other writing materials to write it down. Call 1244 they will voice your number.
How to check AIRTEL phone number
More here https://www.uchehub.com.ng/2019/05/how-to-check-glo-airtel-etisalat-and-mtn-phone-number.html