Phosphorus (P) is an essential nutrient for all living organisms and plays a critical role in biological growth and metabolism. However, at elevated concentrations in aquatic systems, phosphorus can trigger eutrophication, stimulate harmful algal blooms, reduce dissolved oxygen levels, and degrade water quality and aquatic ecosystems. Therefore, accurate and timely monitoring is important for wastewater treatment, environmental protection, and water resource management. Currently, P is detected using bench-scale analytical methods, including ion chromatography, fluorescence spectroscopy, colorimetry, and spectrophotometry, as well as hand-held standard kits that rely on chemical reagents. However, their suitability for on-site, real-time monitoring is limited by high cost, chemical additions, large-scale instrumentation, and complex operational procedures. Therefore, this study evaluates, for the first time, a chemical-free optical fiber-based sensor for phosphorus detection using Fourier Transform Infrared (FTIR) spectroscopy. The objectives are to: (i) determine the detection limit of the coated optical fiber, (ii) evaluate its regeneration performance through repeated sensing cycles, and (iii) investigate the impact of background water quality characteristics (pH, alkalinity, and organic matter) on phosphate selectivity. Preliminary results demonstrate that the coated optical fiber successfully detected phosphate at concentrations as low as 0.01 mg/L as P and exhibited complete regeneration between detection cycles, enabling repeated use while maintaining consistent sensing performance. These findings demonstrate its potential as a sensitive, regenerable, and practical platform for phosphate monitoring. Ongoing work focuses on evaluating sensor selectivity under varying pH, alkalinity, and organic matter conditions. The findings will be presented and discussed at the meeting.