Q: I'm no longer able to facetime one of my contacts from my iphone 6 plus but I still can from my iMac. The facetime icon shows up on my desktop and I can use it flawlessly. But the same contact on my iphone no longer has the facetime option.

I'm no longer able to facetime one of my contacts from my iphone 6 plus but I still can from my iMac. The facetime icon shows up on my desktop for all of my contacts and I can use it flawlessly. But the exact same contact on my iphone - one that has been working fine for years - no longer has the facetime option. The icon is there, but it's not lit up green and I can't choose it. My friend and I spent 30 minutes testing it while I was sitting at my desktop with my iphone in hand. I could call from my desktop but not my phone. No error message, just no option. I did notice that on my iphone under the Facetime settings, my cell phone number is there and checked, but it is greyed out. Don't know what that means or how it changed. Can anyone help? I facetime a lot from my iphone while traveling so I need to figure this out.

27in iMac (late 2013), 10.10.5

iPhone 6 plus, 9.0.2, Verizon service