Description of problem:
The phone number can be updated to empty when we edit the primary contact info, while the phone number item is the required one which cannot be set empty when we register plan subscription.

Version-Release number of selected component (if applicable):
OpenShift Master:v3.9.41
Kubernetes Master:v1.9.1+a0ce1bc657
OpenShift Web Console:v3.9.41

How reproducible:
100%

Steps to Reproduce:
1.Log in openshift account console which has subscribed one paid plan.
2.Click "Manage Subscription" then Click "Edit" beside Primary Contact.
3.Set the Phone Number item empty. 
4.Click "Update Primary Contact"
Actual results:
4.The primary info can be update with empty "Phone Number".

Expected results:
4.The primary info should not be update with empty "Phone Number".The "Update Primary Contact" button should be disabled when the "Phone Number" is set empty value.

Additional info: