Phosphate contamination due to agricultural runoff and urban wastewater is one of the main causes of eutrophication and thus loss of water quality. To combat eutrophication caused by the accumulation of phosphates, it is critical to monitor trace amounts of phosphate in water. While conventional mid-infrared (mid-IR) spectroscopy is able to detect phosphate in a complex matrix due to its chemical selectivity, its sensitivity is limited due to the high absorption of water bands impeding the use of long interaction lengths. To combat this, preconcentration schemes combined with evanescent field spectroscopy aim at enriching the analyte into the probed volume. In this work, we made use of the versatility and defined porosity of the novel material class of metal-organic frameworks (MOFs). The structure of the MOF NH2-MIL-88B(Fe) is tuned to selectively enrich phosphates from the aqueous phase into the confined pores of a thin MOF film coated onto the surface of an attenuated total reflection (ATR) prism. Using this technique, we present a mid-IR based sensing platform, capable of the detection of sub-ppm traces of phosphate in water without the need of extensive sample preparation. We opted for a concept of easy applicable and removable single-use sensing layers on attenuated total reflection prisms to overcome the struggle of desorbing chemisorbed phosphates, while still guaranteeing robust results. For that, a facile, reproducible workflow for the preparation of thin NH2-MIL-88B(Fe) layers onto the ATR substrates was developed. Calibration of the phosphate sensor was performed using aqueous solutions of monobasic phosphate, performing sequential injection analysis to standardise sampling. The sequence included internal referencing of the respective sensing layers to allow for stable results regardless of the applied MOF layer. Calibration curves followed the Langmuir adsorption model, which was used to derive a limit of detection (LOD) of 0.14 mg L-1 phosphorus in water.