Why do I have a black screen and phone is still on?

From the description, either your screen or a component on the motherboard that is relevant to transferring image to said screen may be faulty. If you can make inputs on the screen, this implies that your digitizer (touch component) is fine and that perhaps the screen itself is as well. If no aspect of the screen inclusive of image, backlight, or touch is working despite your phone being active, this lends itself more to the issue being the screen itself, as the digitizer and display have separate connectors and would not necessarily become faulty together as a result of an issue on the motherboard. I recommend troubleshooting the issue further to be sure.

This iFixit guide goes over the screen replacement process if that's an option you'd like to take.

I hope you manage to solve the issue without too much trouble.