Hey guys.....This is SOLVED PS 1.7xx !!
I found the answer to this question, I was having the same issue with the phone number, I wanted the phone # mandatory.
No coding need, just a simple checked mark is needed.
In your BO > Customers > Addresses> @ the bottom of your customer list
there is " + set required fields for this section" click that button.
Check all fields you need, including phone number!!
Only took me 2 weeks to figure this out. I couldn't find this anywhere.
Hope this help.