My back arrow on my iPhone 13 is not working. I turned off my phone and restarted it. Still, not working

Please post screen shots with examples. That is not a universal feature of ios. There is no ‘back button’ in the upper left corner. The only thing close would be an option to return to the previous app IF the app you are in now was launched by the previous app automatically.

What “back arrow” are you referring to? Since there are no dedicated buttons/touch points on the face of an iphone, what and where this is will be dependent on the application you’re in.