In this study, a glaze slurry was prepared with different contents of tricalcium phosphate. It was then applied to a fly ash microcrystalline ceramic billet and sintered at 1180 °C for 30 min to prepare the complex. The aim was to obtain a high value-added application of fly ash in order to reduce environmental pollution. The study systematically investigated the influence of the Ca₃(PO₄)₂ content on the crystal phase evolution, physical-mechanical properties, and micro-morphology of the complex. The results showed that products sintered at 1180 °C with 8 wt% Ca₃(PO₄)₂ demonstrated better performance, with a water absorption of 0.03% and a Vickers microhardness of 6.5 GPa. Additionally, the study observed a strong correlation between the Ca₃(PO₄)₂ content and the opacity effect. A feasible opacity mechanism was also proposed to explain the variation of glaze colors and patterns with different contents of Ca₃(PO₄)₂.