The aim of the study was to determine the phosphorus removal efficiency of Rockfos® material used to fill a full-scale meander-flow P-filter. This filter is the final element of a hybrid constructed wetland wastewater treatment plant located in Białka, Dębowa Kłoda commune in southeastern Poland. During the May 2022–July 2025 study, phosphorus removal efficiency and pH changes were analyzed based on wastewater analysis before and after the P-filter. Additionally, extended wastewater analysis was conducted between August 2024 and July 2025, including analysis of total suspended solids, chemical oxygen demand (COD), biochemical oxygen demand (BOD5), electrolytic conductivity, and total nitrogen. The phosphorus removal efficiency of the meander-flow filter during the full study period was 44.43%. Statistical analysis showed a significant effect of P-filter on pH, turbidity, conductivity, and changes in phosphorus concentrations, total alkalinity, and BOD5. No significant effect was found on total nitrogen and COD.