How does an iPhone import photos from the photo stream? If I put a picture on my Mac to photostream and it moves to my iPhone's photostream and I delete the picture from my photostream on my Mac, will there still be a picture left on the iPhone in the camera roll?
No.
When you delete an image from Photo Stream, there is a message (at least on iOS) that says something like

The image will disappear from Photo Stream on all your devices.

Hence, deleted means no longer in Photo Stream anywhere.