Some iPhones in middle eastern countries are not allowed to support FaceTime:
Get help with FaceTime on your iPhone in Saudi Arabia - Apple Support
FaceTime isn’t available or might not appear on some iPhones and iPads purchased or used in Saudi Arabia, Pakistan, and United Arab Emirates, including Dubai. However, with iOS 11.3, FaceTime is available on iPhone in Saudi Arabia.
https://support.apple.com/en-us/HT204170
It does not matter what country you are in - if the country where the iPhone was originally sold does not support FaceTime, it cannot be added.