How to make the phone number of the candidate as mandatory in the agency page create candidate

Summary:

Folks, Any inputs on this, tried doing it through Sandbox by making Phone Number mandatory in Define Application Flow Required fields, but still its not reflecting on the Agency Page. When the Agency is creating a candidate Phone number is not mandatory. Our customer would like to have this as mandatory field. No option found in VBCS as well. Any alternate options do we have here.

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

26C

Code Snippet (add any code snippets that support your topic, if applicable):