Can candidate be referred without emailid?

Summary:

Content (required):

Currently email address is mandatory while referring a candidate . Can we make phone number as mandatory as blue-collar employees doesn't have emailids?

Navigation - Me>Opportunity Marketplace>Select a job>Click on Action button>Click Refer Candidate.

I have checked in HCM design studio there is no option to add phone number as mandatory. Is there any alternate workaround for this requirement.

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

23C

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