An activator’s selective occupation of a host is of great significance for designing high-quality white light-emitting diodes (w-LEDs) phosphors, while achieving a full-spectrum single-phase white light emission phosphor is challenging. For developing high-performance and green-emitting phosphors with narrow bands used for backlight display, a series of Na2Mg1-xAl10O17:xMn2+ (NMAO:xMn2+) phosphors with high Mn2+ concentration were synthesized. The NMAO:0.65Mn2+ green phosphor exhibits an ultra-narrow band green emission with full width at half maximum (FWHM) about 27 nm and peak position at 513 nm when excited by the blue light with wavelength of 450 nm. The NMAO:0.65Mn2+ not only has a super narrow band which is narrower than β-SiAlON:Eu2+ (FWHM ∼ 55 nm) but also shows an exceptional thermal stability performance (77% peak intensity @423 K). A w-LED device was assembled with NMAO:0.65Mn2+, a blue GaInN chip and K2SiF6:Mn4+ phosphors, which represents a wide color-gamut of 112% National Television System Committee (NTSC) standard under the current of 50 mA. These results demonstrate the NMAO:0.65Mn2+ has potential superiority in application of backlight display.