There are three main shot sizes we need to think about when telling story: Long, Medium, and Close.
Long shots (also commonly called Wide shots) show the subject from a distance, emphasising place and location, while Close shots reveal details of the subject and highlight emotions of a character. Medium shots fall somewhere in between, putting emphasis on the subject while still showing some of the surrounding environment.
When filming on an iphone we will typically only have one lense. although we do have a zoom function on the camera its not an actual optical zoom using the lense but a digital zoom. So with iphone footage when you use the zoom function you are actually just closing in on the footage the camera is taking. So the more you zoom the lower the resolution of the image you are shooting. Large zooms do start to pixelate the subject and give grainy looking footage. So for the best quality footage, if you want to make your subject larger in the shot, you need to physically move the camera closer to the subject to frame it the way you want to. Dont use the digital zoom function!
As a film maker and story teller you c an mix together long shot, medium shot and close up shots to keep the user interested and to direct their eye. Typically most scenes will start with an establishing shot that sets the overall scene and location the sotry or scene will occur in. You can then mix between medium shots to give more detail and close up shots to focus on important details. The idea is to mix up these shots to tell the story and keep the audeinces perspective changing. Doing this will help to engage the audeince and stop them getting board.
Try to watch how short bulletins on your local news station make use of long shots medium shots and close up shots to engage the audience. Very few shots will be held for more than a few seconds.