There is no FaceTime app for the iPhone. FaceTime, on an iPhone, is accessed through the Contacts app. You tap the FaceTime ico to make a FaceTime call. Is FaceTime turned on/activated: Settings>FaceTime>On. Do you have that Setting? If you don't have that Setting, where did you get your phone? In a few countries FaceTime is banned, and if you obtained your phone from one of these countries, you won't have that Setting, & there is no way to add FaceTime to your phone.