Spend enough time shooting with your DSLR or mirrorless camera, and operating it becomes muscle memory. Your fingers know exactly where to press, toggle, or tap to change ISO, switch shooting modes, set your autofocus, or change any number of settings. With a little practice, you won’t even need to look away from your subject matter while you’re shooting — and you’ll never miss a shot. As a plus, many of these buttons are customizable, letting you program the most useful camera functions (like back-button autofocus) to be within instant reach (via Improve Photography).
Smartphones are meant for many things besides just taking photos, so they inherently lack the controls needed to quickly manipulate whatever camera settings are available to you. At least, these controls aren’t as easily accessible as they are on a camera with a dedicated shooting mode dial, ISO button, autofocus point selector, and so on. The iPhone, for example, takes a couple of taps within the camera app to uncover options for changing the exposure, f/stop, flash, or self-timer.