Call barring service code for iPhone 15 pro

Contact your carrier as that is not a device feature, it is a carrier feature for using a service code. For some it is *33# to turn it on and #33# to turn it off, but again that depends on your cellular provider.

Call barring isn't a built-in feature on iPhones, including your iPhone 15 Pro. Instead, it's managed by your mobile carrier.

Probably, you may need a third-party call blocker app. Check it under Settings > Phone > Call Blocking and Identification.

See the pic below

This blocking is allowed by the Carriers in India. Example of Airtel (Private) & BSNL (Govt Owned) & Vodaphone is given below

• Airtel: airtel: Prepaid | Postpaid | 4G | DTH Services in India - Airtel
• BSNL: Activate BSNL DND (Do Not Disturb) to Avoid Marketing ...
• Vodaphone: Do Not Disturb Registration Online | DND Activation - Vi