Why is there a blue line across my phone screen

@albert2625 most likely a display fault but can be related to a bad ribbon cable to the display or a bad connector. Check the cable for tears, corrosion etc. Then check the connector for bend, broken, corroded pins etc. It all of this checks out, I would suggest to replace the display. Since iFixit does not yet have a guide for that, use something like this video If you prefer written instructions use the ones from here Replacement display are readily available at many online stores. Just make sure you purchase one for your version of the the phone.

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.