@Athira Chandran Thanks for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this.
Unfortunately, acquiring a phone number for the subscriptions whose billing address is in India is not possible. You can refer here for more information about the list of supported country/regional availability of phone number based on subscription type.
ACS provide a trail phone number which is also limited for the subscription whose billing address are based out of United states only as mentioned here.
Also, you cannot change/update the country or region in billing address of an existing account you need to create another account with different address and then contact Azure Support for further assistance in transferring your subscription to the new account.
Refer to this billing documentation for more information about it.
Hope this is helps, let me know if you have any further questions on this.
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