Besides using Portrait Mode, what is a key physical technique involving subject-to-background distance and lens choice to maximize the shallow depth of field effect when capturing a photo or video with an iPhone?

Shallow depth of field refers to the photographic effect where a very small portion of the image, typically the main subject, appears sharp and in focus, while the areas in front of and behind the subject are increasingly blurred. This selective focus draws attention to the subject by isolating it from its surroundings. To maximize this shallow depth of field effect on an iPhone without using Portrait Mode, a key physical technique involves two main adjustments: subject-to-camera distan....