How to make a photo into a video on iPhone?

Basically for an Instagram post I just want an album cover but I want it to be good quality so I don't want to just record the physical cover. I already know how to make the video but the problem is the program requires it to already be a video so I'm trying to convert the photo into a video somehow without using a computer. I already tried using a.gif file but It didn't work and there aren't any screen recording apps