Herein, a series of three-dimensionally ordered macroporous (3DOM) Bi₄O₅Br₂ photocatalysts with different macropore sizes were successfully fabricated via a polymethyl methacrylate (PMMA) template method. The photocatalytic activity for phenol degradation over 3DOM Bi₄O₅Br₂ first increased and then decreased with the rise in macropore size. Specifically, 3DOM Bi₄O₅Br₂-255 (macropore diameter ca. 170 nm) exhibits the best photocatalytic activity in the static system, which is about 4.5, 7.3, and 11.9 times higher than those of bulk Bi₄O₅Br₂, Bi₂WO₆, and g-C₃N₄, respectively. Meanwhile, high phenol conversion (75%) is also obtained over 3DOM Bi₄O₅Br₂-255 in the flow system under full spectrum irradiation. Furthermore, 3DOM Bi₄O₅Br₂-255 also shows strong mineralization capacity owing to the downward shift of valance band position (0.15 V) as compared with Bi₄O₅Br₂. Total organic carbon (TOC) removal rate over 3DOM Bi₄O₅Br₂-255 (62%) is much higher than that of Bi₄O₅Br₂ (17%). The enhancement in photocatalytic performance of 3DOM Bi₄O₅Br₂-255 is attributable to its better phenol adsorption, O₂ activation, and charge separation and transfer abilities. This work combines the advantages of 3D structure and surface dangling bonds, providing new possibilities for designing highly efficient photocatalysts for pollutants removal.