Phenols are well-known noxious compounds, which are often found in various water sources. In this research, a new method was used to determine the total phenol and measure the biological activity, by using the microfluidic paper-based (µPAD), smartphone Sensor. It is portable, low-cost, and environmentally friendly. The paper was prepared using filter paper by cutting method. The reagent was dried on the paper. The color sensor of the smartphone device was used as the color intensity sensor of the samples through the images captured by the smartphone through software downloaded to the phone. The focus of the samples is measured from the RGB value of the images taken from the (iPhone 14) device, where each image represents a specific focus. The calibration curve for this method was in the range of M (0.00016–0.5), the correlation coefficient (R2) was equal to (0.9753), the limit of detection was in the amount of (0.000032) M, and the relative standard deviation (RSD%) for the concentration is (0.02) M, for which the examination was repeated (10) times and its value was (0 %), and the recovery value (Recovery%) was equal to (100 %).