Phosphors have wide applications in many industries, especially the automotive industry. Low efficiency and complex production methods are current challenges of phosphor packaging technology. In this study, M2Si5N8:Eu2+ (M = Ba, Sr) phosphor ceramics (PCs) were developed that exhibited excellent thermal quenching characteristics and a broad wavelength range—580 (yellow)–620 nm (amber)—for use as automotive amber light-emitting diode (LED) light sources. Phosphors— M2Si5N8:Eu2+ (M = Ba, Sr)— with various Ba:Sr compositions were synthesized at 1600°C. These phosphors were, in turn, used to fabricate PCs; pressureless sintering was aided by the addition of a MgO/CaO—70:30—mixture. The density, microstructure, and optical properties of the phosphors and PCs were analyzed. When the molar concentration of Sr was 0.2 mol, the corresponding phosphor wavelength was 593 nm; these optical characteristics are suitable for amber LED applications. The PC containing 5 wt% sintering aid showed a density of 4.187 g/cm3 and relative density of more than 99%. These sintered PCs demonstrated excellent adaptive optical characteristics that can be used to great effect in automotive LED applications.