Subject pretty much sums up the issue.
Endpoint URI tested:
https://platform.ringcentral.com/scim/v2/Users
https://platform.ringcentral.com/scim/Users
https://platform.ringcentral.com/scim/v2/Users/.search
The endpoint https://platform.ringcentral.com/scim/v2/Users/id does return the phoneNumbers array, both the assigned phoneNumber (DID) and assigned extensionNumber values.
Is there a reason the ~/scim{/v2}/Users{/.search} endpoints do not return the PhoneNumbers array?