<p>Cotton fabrics are extensively used for their comfort and biodegradability. However, their flammability presents a significant fire risk, necessitating the urgent enhancement of their flame-retardant properties. Phytic acid, a natural compound with high phosphorus content, offers potential as a flame retardant but has limited efficacy. The incorporation of metal ions, such as zinc, can synergistically enhance its performance. Foam finishing is a low-fluid, energy-efficient process that demonstrates significant advantages over conventional finishing techniques in terms of resource utilization and performance efficiency. This work developed highly flame-retardant cotton textiles using a green, low-additive liquid foam finishing technique by combining phytic acid and zinc acetate. The synergy between phytic acid and zinc ions significantly enhanced charring ability and flame-retardant performance of the fabric, achieving a limiting oxygen index (LOI) of 32.5% and reducing the char length to 4.3 cm. It is particularly noteworthy that this method utilizes biomass materials as both the flame-retardant finishing agent and the foaming agent, without the use of organic solvents or hazardous chemicals throughout the process. While achieving excellent flame-retardant performance, it effectively preserves the softness and comfort of the fabric, thereby combining environmental friendliness with high application efficiency. This study integrates foam finishing with biomass-based flame retardancy, proposing a simple, eco-friendly method aligned with sustainable development principles, and demonstrating strong potential for large-scale production of flame-retardant cotton fabrics.</p>