Phosphorus-doped porous carbon materials, sourced from biomass, are becoming increasingly recognized as excellent electrode materials for zinc-ion hybrid supercapacitors (ZHSC). However, existing fabrication methods often involve complexities, a reliance on specialized equipment, and high costs. In this study, we successfully used bamboo fibers and phytic acid to prepare phosphorus-doped porous carbon with a high specific surface area. Our method, which takes advantage of the flame-retardant effect of phytic acid on biomass, eliminates the need for additional water removal steps or pore-forming agents. As such, it offers benefits such as simplicity, cost-effectiveness, environmental sustainability, and adaptability, relying solely on biomass for phosphorus doping and pore formation. The resulting phosphorus-doped porous carbon has a high specific surface area of up to 1229 m2 g−1. Correspondingly, the ZHSC fabricated using this carbon reaches a specific capacity of 109 mAh g−1 in a 2 M ZnSO4 electrolyte. Additionally, a quasi-solid-state flexible ZHSC based on this carbon was successfully manufactured, achieving a maximum energy density of 60 Wh kg−1 and a maximum power density of 1653 W kg−1. These performance metrics surpass those of some similar ZHSCs, underscoring the efficacy of our material fabrication method in producing superior electrode materials for ZHSCs.