Phone screen black but randomly coming on with light lines across and-

“is there any way of fixing this problem without getting it repaired?”

By that logic, you don’t want it repaired lol. Anyways, I see this happen quite often with the X series and above that use OLED panels. They either go bad on their own or, in your case, suffer a bit of liquid damage and then die. Good news is, it should be fixable so long as there’s no underlying issues with the device meaning there isn’t any other internal damage either caused by dropping it or liquid damage. You’ll need to get the screen replaced. You can order a kit from ifixit and attempt it yourself and your own risk, or if you don’t feel comfortable performing such a repair, you can take it to a reputable repair shop that would be more than happy to fix it with good experience and knowledge. I would avoid an LCD replacement if you can. Remember, iPhones are premium devices. There’s a reason why apple charged so much when that phone was new and it’s certainly not because they used cheap parts. I would highly recommend a soft OLED panel as that’s as close to factory as it will get. Then there’s hard OLED which you can get away with but the panel is a but more fragile. Just beware that any repairs completed either by you or a repair shop will have to break the liquid resistant seal. It can be replaced but it’s not as good as the factory and just like Apple, a lot of us won’t guarantee that seal.