What device is primarily used for audio playback in mobile devices?

The device primarily used for audio playback in mobile devices is the speaker. Speakers convert electrical signals into sound waves, allowing users to hear audio from their devices, such as music, phone calls, or notifications. In mobile devices, built-in speakers enable users to enjoy audio without needing additional equipment.

While headsets can also be used for audio playback, they are primarily designed for personal listening and may require a connection to the mobile device. Microphones and webcams serve different functions, being used for audio input and video capture, respectively. Thus, speakers stand out as the primary component for audio output in mobile technology.