Organophosphorus pesticides (OPs) are of great concern due to its potential harms on human health and the environment. Herein, a budget-friendly, rapid and convenient colorimetric sensing platform is developed for detection of OPs in the environmental and food samples. The sensing element, PANI-MnO 2 nanozyme with excellent oxidase mimetic activity is synthesized at room temperature, which is able to directly oxidize 3,3,5,5-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB (OxTMB) within 2 min. Ascorbic acid (AA) can inhibit the oxidization reaction of TMB, consequently causing the blue color fading. Ascorbic acid 2-phosphate (AAP) could be hydrolyzed to produce AA by alkaline phosphatase (ALP). In the presence of OPs can effectively decrease ALP activity, resulting in the recovery of catalytic activity of PANI-MnO 2 . Therefore, sensitive and selective OPs detection is achieved. Under the optimal conditions, excellent detection performance in term of glyphosate as a model is achieved with a linear range from 0.50 to 50 μM, the detection limit is 0.39 μM (S/N = 3). The utility of method is further improved by combining a portable smartphone platform with a color picking application. The colorimetric platform achieves instrument-free detection of OPs and overcomes the uneven color distribution of traditional paper-based chip, providing an alternative strategy for the qualitative discernment and semi-quantitative analysis of OPs on-site.