@nprofile1q... That's pretty much how LED room lighting works: LEDs behind phosphor.
But how would you scan a phosphor screen with that? LEDs don't put out a beam that can be deflected with electromagnets. They emit light in all directions.
There are screens where there's an LED for each RGB subpixel, namely OLED and MicroLED. No phosphors or scanning involved there, though, just a grid of LEDs.