Chosen Solution
The phone started by coming on after letting it sit for a while (it would have a small amount of light at the top of the display). After it finally came up, the phone would function for a while with the backlight flashing every now and then. Now I can get the screen to come on other than the faint light at the top of the screen.
This is usually caused by either a loose connection from phone to screen, blown backlight circuit or liquid damage near the screen connector, or just simply a faulty screen needing replacement. First thing I would try is reseating the screen cables, next inspect the screen connector on the board for physical damage or signs of wear and tear as this can cause a bad connection to the screen ribbon cables. Worst case scenario, phone has liquid damage near screen connectors / backlight circuit blown meaning you would need to take the phone to a reputable repair shop that does board-repairs on iPhones. Follow up to step 21 of this guide on how to unplug the screen cables: iPhone 6s Screen Replacement iPhone 6s Screen
Have you damaged the screen or attempted any repairs recently? Sounds like a damaged Logic board, but coule just be the digitizer
