The function of an operating system in a smartphone is to manage hardware and software resources, providing a user interface and enabling applications to run effectively. The operating system acts as an intermediary between the user and the device's hardware, handling tasks such as memory management, multitasking, and device coordination. Popular smartphone operating systems like Android and iOS offer various features and functionalities, allowing users to install apps, customize settings, and perform daily tasks. Overall, the operating system is vital for ensuring a smooth user experience.