@narimacna this sounds like either a bad LCD flex or a bad LCD. You can take it apart and check your flex cable and the connector for tears, debris or corrosion. Ultimately so, it sounds like you will need a new display.
Use something like [https://www.youtube.com/watch?v=aw6n7cmSzl4|this video] to repair your assembly. While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.