No call blocking option on my iPhone

To add a contact, from Messages or FaceTime, go to Settings > Messages or Settings > FaceTime, tap Blocked Contacts. Then scroll down, tap Add New, then select the contact that you want to block. To add a contact, from Mail, go to Settings > Mail, then tap Blocked.

Block phone numbers, contacts, and emails on your iPhone ...

1. Is this your corporate iPhone? Then please contact the system administrator of your corporate
2. If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you