@Oleksandr Petrovskyi Connected offline, reviewed the issue and researched internally on this, found this issue with phone number validation during Azure Subscription Sign up can be resolved by creating a support ticket and working with our Azure subscription team.
So suggested to use one of the contact numbers from here - https://support.microsoft.com/en-us/topic/global-customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2 and created a support ticket.
Initially the ticket was routed to incorrect team, made sure this was transferred to subscription team and got the account unblocked, so there after sign up process was completed successfully.
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