Can you replace screen with glass part or do you need LCD?

It is possible. However it's a lot of practiced work. I buy digitizer LCD assemblies, and then put shields and camera, mic, prox sensor assemblies on them. It takes my repair time for a display assembly down to about two mins. If you're really trying to save money, which you will have to spend money to get at a comfortable level, to just replace the digitizer. You could do it. However, you'll need weeks of practice, before you're display assemblies come out looking semi-professional. You can also buy a frame that will hold all these things in place. Which will make this easier. iPhone uses OCA glue. Android uses LOCA glue