LEDs emit light in a narrow frequency band, i.e. LEDs have intrinsic colors. White is not just one color, so your options to make white light from LEDs are: 1)

LEDs emit light in a narrow frequency band, i.e. LEDs have intrinsic colors. White is not just one color, so your options to make white light from LEDs are: 1) Use multiple colors of LEDs, which will make the light source look white but objects lit by this source will have off colors. 2) Use a phosphor coating on the LEDs, where the phosphor absorbs (most of) the narrow frequency band output by the LEDs and emits the color(s) that you want. In this case, they went with option 2 with a phosphor that absorbs blue light and emits broad spectrum white light.