A cobalt-based electrochemical voltammetric sensor for rapid phosphate detection in wastewater was evaluated in terms of its operational envelope, impact of pH, detection limits, linearity of response, accuracy and reproducibility in a single ion solution. A dynamic linear range was measured between 6 and 100 mg P/L, with a detection limit of 6 mg P/L at pH 8. pH and ions such as Cl^-, SO₄^2-, NO₃^- in addition to dissolved oxygen (DO) all influenced the current response. Tests on real wastewater samples verified the effect of the interfering factors, as phosphate measurements from three different sampling points (influent, activated sludge mixed liquors and effluent) did not correlate with standard methods. The success of cobalt-based sensors will depend on the simultaneous measurement of, or the calibration for interfering parameters. Despite these challenges, a clear linear response to phosphate was achieved at relevant concentrations in wastewater and the sensor may yet form part of a real time control system because of its rapid response time, lack of reagent requirement and potential low cost.