Why is my Facetime camera always off during calls?

When i’m on facetime with anybody and i go out of the facetime app my phone doesn’t have the little screen in the corner ever, i don’t know why it turned off but it’s been like this ever since i broke my camera on like my i phone 6 and i’ve had multiple new phones. Is there any way to get the screen or do I have something disabled? I open settings and there’s no way to turn it on.

[Re-Titled by Moderator]