Just how good is the iPhone's camera function? If you compare it to a $1,000 plus digital SLR, then the truth is it is a very inflexible piece of kit. The literal "point and click" camera with absolutely no user control.
Even so, given the right conditions, the iPhone can take reasonably good photos. Ideally the sun should be behind the camera and the range of light contrast should not be too great. For example, two thirds sky will bias the exposure setting, making the landscape or headshot much too dark.
This is an example of what can be achieved.