I wrote a very small and unfinished game in python using pygame. Is there an easy way to convert this to an app which I can use and test on my iPhone without rewriting the whole code in things like kivvy?
There isn't an easy way, it's impossible transform the code.
But for an easy and not professional game, you can try to do this.
Use a site for hosting the game like Python Anywhere (free).
Now create an app without any coding skill.
I never use IOS, for android MIT Inventor is a good framework for create apps.
For Ios, you can try Appypie or Appyourself, but you can find other better alternatives.
The app must contain a web-browser viewer with your site.
The app shows a web page with your game in it.
I can't imagine another way, it's a bit difficult and the app require internet connection.
Good luck!
How to convert pygame application to iOS app