Hello Tanushreee,
Credit Card is a mandate for signing up for Azure Subscription. One of the ways we keep prices low is to verify that account holders are real people, not bots or anonymous trouble-makers. We use the phone number and credit card for identity verification.
We do not charge your credit card anything, but you may see a Rs 2 verification hold on your credit card account, which is removed within 3 to 5 days by your bank.
Reference link: https://support.microsoft.com/en-in/help/4467267/can-t-sign-up-for-azure-in-azure-portal-or-azure-account-center
Regards,
Shubham Agarwal