If there were iOS dev tools on the iPhone, I think they’d probably be built around Xcode’s Interface Builder and resemble something like a touch friendly versio

If there were iOS dev tools on the iPhone, I think they’d probably be built around Xcode’s Interface Builder and resemble something like a touch friendly version of Visual Basic or REALBasic, simply because the smartphone typing experience is so ill-suited for writing code. On iPad there’s Playgrounds, which is kind of an Xcode Lite that supports Swift and SwiftUI but to do anything substantial with it you’re going to want a physical keyboard of some kind.