Red-emitting phosphor-in-glass (PiG) materials with a high luminescence efficiency were developed by co-firing commercial red-emitting (Sr,Ca)AlSiN3:Eu2+ (SCASN) phosphor and our original glass frits with a composition of Li2O-Na2O-ZnO-Al2O3-B2O3-P2O5, which has a low Tg (271°C) and Ts (380°C) temperatures. By optimizing the sintering temperature and the content of the phosphor, the highest luminous efficacy was obtained for the 3 wt.% SCASN-based PiG sintered at 400°C, which showed a luminous efficacy of 25 lm/W rad by combining the PiG materials with a blue light-emitting diode (LED) chip-on-board (COB, incident power = 100 mA). The internal quantum efficiency of this sample under excitation at 450 nm was 53%. The PiG-based LED maintained a high luminous efficacy when the incident power of the blue COB increased up to 5.5 W (47 lm).