Mobile phone use is pervasive, yet little is known about task switching on digital platforms and applications. We propose an unobtrusive experience sampling method to observe how individuals use their smartphones by taking screenshots every 5 seconds when the device is on. The purpose of this paper is to incorporate the psychological process into feature extraction, and use these features to effectively predict the task switching behavior on smartphones. Features are extracted from the sequence of screenshots, gauging visual stimulation, cognitive load, velocity and accumulation, sentiment, and time-related factors. Labels of task switching behavior were manually tagged for 87,182 screenshots from 60 subjects. Using random forest, we demonstrate that we can correctly infer a user's task switching behavior from unstructured data in screenshots with up to 77% accuracy, demonstrating it is a viable option to use features of the screenshots to predict task switching behavior.