Is it hidden via Settings > General > Restrictions > FaceTime being set 'off' ? On an iPhone you don't get a separate app for it, instead you get a FaceTime button on a contact's page e.g. in the Contacts app or via the Contacts tab in the Phone 'app'.
If it doesn't appear in Restrictions then where was the phone bought ? It's not available on devices sold in the UAE, Saudi Arabia, and possibly a few other countries.