A porous boron nitride (p-BN) filler network was fabricated to overcome the limitations of existing phase-change-material (PCM) composites. The novel p-BN network was prepared by freeze-casting and BN synthesis by calcination. Thermally conductive sodium acetate trihydrate (SAT) composites were fabricated by dip casting and hot-pressing using a hybrid filler system of p-BN and raw BN. The prepared SAT/p-BN/BN composite exhibited a latent heat of 112 J/g, high thermal conductivity of 4 W/mK, and 548% higher tensile stress. The SAT/p-BN/BN composites can be used to realize efficient thermal management by combining the heat saving and heat dissipation enabled by large latent heat and high thermal conductivity. In other words, the fabricated PCM composites can promote the development of battery thermal management systems.