Apple’s iOS is what is found on every iPhone. As of 2019, the latest version was iOS 13. A new version is released in Q4, while it’s announce in late Q2 at WWDC with a developer and open beta following in Q3.
iPhone 13 prototype shows an under-screen camera, in-display Touch ID and a USB-C port
This iPhone 13 prototype is reportedly among many other models that are currently being tested, so the final design might vary in the end.