This is actually a great question to ask. I took a moment to research and see if it is possible for you to be able to play any other VNs on your iPhone. (I have my iPhone too, it would be so nice to make this come to reality!)
https://www.reddit.com/r/RenPy/comments/o2sjtr/ios/
This is what I found- and checked with Ren'Py website. So far, this appears that I would need to create iOS distribution version. As a developer myself, I could honestly make this happen just for you and probably others who stop by. My only concern is that it mentioned several drawbacks when creating the iOS version, this is something I have to try and test to make sure it really works.