Bio-derived phytic acid exhibits great potential to improve the flame retardancy of textile materials, but it has poor washing durability. In order to address this problem, an efficient, reactive, and phosphorus-containing flame retardant (FR) HPPHBTCA was synthesized using phytic acid, pentaerythritol and 1,2,3,4-butanetetracarboxylic acid, and the chemical structure of HPPHBTCA was characterized. HPPHBTCA was applied to develop FR functional wool fabric, and its FR efficiency and washing durability were evaluated. The wool fabric treated with 0.14 mol/L HPPHBTCA had self-extinguishing performance even after 20 washing cycles during the vertical burning test, presenting good FR ability and resistance to washing. The catalytic char-forming effect of HPPHBTCA contributed to the enhanced FR and smoke suppression properties of wool fabric, and the ester bonds formed between HPPHBTCA and wool fiber resulted in the good washing durability. The HPPHBTCA treatment had a negligible effect on the whiteness, tensile strength and handle of wool fabric. This study offers a novel route to prepare the eco-friendly and durable FR agent using natural and phosphorus-containing compound.