Blue laser diodes (LDs), owing to their high electro-optical conversion efficiency, strong directivity, and small size under high power, have paved new paths in the semiconductor lighting and display industry. Blue LDs are expected to replace LED lighting in laser displays, automotive headlights, and other advanced lighting fields. In this study, the Lu3Al5O12: Ce3+ phosphor-in-silica glass (LuAG: Ce-PiSG) is fabricated using spark plasma sintering at 1060 °C. This method enables rapid sintering while maintaining the stability of the silica glass matrix, resulting in high transparency and minimal destruction of the crystal structure of the LuAG: Ce phosphor. The phosphor-converted LDs made from LuAG: Ce-PiSG exhibit high luminous efficacy (298 lm·W−1) and luminous flux (1069 lm). The results show that LuAG: Ce-PiSG has significant potential for application as a robust, high-efficiency phosphor conversion material for high-brightness laser lighting applications.