I lost my apple ID number.......
I can't access my number anymore for authentication
iPhone XS Max, iOS 14
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If you mean the number where you receive 2 factor authentication responses tap or click on the “didn’t get code” and you will see a list of other trusted numbers and/or devices that you hopefully set up. If you didn’t set up any you will have to initiate Account Recovery→How to use account recovery when you can’t reset your Apple ID password - Apple Support
If I have not read your mind correctly please explain what you need to know.