This “No light on display” is usually an internal issue with the LCD connector. However, Apple recommends some processes to practice on your phone to make sure the black screen is not a software glitch. The phone has calls, notifications but doesn’t show anything on display. The Phone display boots up with an Apple logo but doesn’t get past the black screen. iPhone can charge (you can hear the sound that the phone makes while charging) but won’t show anything on the display

Force Restart your iPhone

Connect the lightning cable, charge it for 10 minutes. Then try force restarting the iPhone

UNCONVENTIONAL: But press the screen into the phone so it may reconnect any dislodged LCD connector. This fix is not recommended however it resolved a lot of the user's Black Display issue