Field of View -  The field of view is how much of a scene is filling the sensor and creating the image from a particular vantage point. When standing in one spot and not moving forward or backwards, your field of view is determined by a number of technical factors such as the focal length of the lens and the size of the sensor. Your field of view can be adjusted from one vantage point by using a form of Zoom, either optical with a change of lens, or digitally, which involves cropping the image and therefor a reduction in resolution. 

Optical Zoom is applied when the focal length of the lens used is adjusted in order to bend and focus the light to fill the sensor with different parts of the scene. You can either use a zoom lens for this or you can switch lenses if your camera allows this. Optical zoom has no impact on resolution as the full sensor is used, however it does have an impact of how the image and objects can look. Some newer phones have multiple lenses which facilitate different fields of view, such as a wide angle lens, and extra wide angle lens or a portrait lens. You can also buy lens adapters for phone which either clip on or are attached via a case, some of which are actually quite good quality.

Phones with multiple lenses, such as the iphone pro models offer a number of different focal lengths, resulting in different fields of view. 

Bare in mind the visual effect of using the different lenses to create the same composition, as the results will be very different. Choose the lens which more effectively portrays your subject and tone.