Smartphones have revolutionized multitasking across various aspects of life but can also pose risks, particularly to pedestrian safety. Research shows pedestrians' smartphone use during road crossings contributes to accidents and fatalities. Studies reveal that slower walking speed and decreased awareness due to smartphone multitasking heightens collision risks. This study investigates the relation between smartphone multitasking behavior and walking behavior of pedestrians, exploring the mediating role of deep task engagement or cognitive absorption. The experiment utilized a smart garment to capture real time physiological data along with self-report measures to gauge the impacts of smartphone multitasking. Participants undertook tasks with different multitasking levels while walking in a gymnasium. Results suggest certain task types increase cognitive absorption, highlighting the need for pedestrian caution during specific multitasking activities. Furthermore, heightened cognitive absorption reduces walking cadence. This study enhances comprehension of cognitive absorption during smartphone multitasking, shedding light on its influence on walking behavior.