Phenolic resin-based ablative materials have gained significant attention in the aerospace sector in recent years. In this study, TGA-DSC, FT-IR, XRD and XPS were employed to the thermal stability and phase transformation of the ZrSi₂–B₄C modified quartz fiber/boron containing phenolic resin (QF/BPR) composite. The compressive failure behavior of the composite at 600–1200 °C was studied through SEM and high-speed camera techniques. The results indicated that the compression strength of the composite decreased to a minimum at 600 °C and increased at 800–1200 °C. The composite exhibited different failure modes at different temperature: shear fracture at room temperature (RT), debonding of the fiber bundles at 600 °C, fiber buckling and fiber shear fracture at 800 °C, fiber buckling and delamination at 1000–1200 °C. The improvement in thermal stability of composite was primarily attributed to the formation of ZrO₂, SiO₂ and B₂O₃, which covered the fiber and effectively transmitted the load, leading to an enhanced strength of the interface between the fiber and resin.