Why is the primary contact's phone number hidden for agents?

When an HR HelpDesk agent accesses the details of a service request, they should be able to view the primary contact's phone number. However, this number is completely hidden by asterisks *******
The same agent who cannot see a contact's phone number from the details of a service request still has access to this same data for the same contact by searching for the contact via the HCM global search bar.
With an administrator profile, the phone number is not hidden.

How can the phone number be made visible to agents?

Agents already have the following privileges:

Manage Person Phone
Access Person Contact Information by HR