Thank you for post!
I am sorry to hear that you are facing an issue which relates to authentication error when login to azure portal and having trouble validating your phone number for your Azure account
Based on the error code AADSTS50020 occurs when a user tries to access a resource in a tenant where their account does not exist.
which means you might log in to Microsoft Entra admin center by using personal Microsoft Accounts which has no subscription.
To fix this issue Create an Azure account with a new tenant
The other side about the validating your phone number, if you have used you phone number or credit card or email earlier in azure it will not allow to create the azure subscription with same details.
Please try to use alternate phone number and see if the issue fixed.
Reference: Error AADSTS50020 - User account from identity provider does not exist in tenant
Hope this helps. Do let us know if you any further queries by responding in the comments section.
Thanks,
Akhilesh V.
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