Cell phone cameras are getting better and better each year as sensor technology improves, but zooming still doesn't really work. Yes, you can "zoom in" with your iPhone, but it's not a real optical zoom. Really, you are just cropping into your picture or video, which means the further you "zoom," the lower resolution you will end up with.
The obvious workaround for this issue is to add a mechanical, moving lens element to one or more of the glass elements in front of the sensor. This would allow the phone's camera to actually zoom in optically. Sadly, there just isn't enough room for this.