How can I view (not download) iPhone pictures on a Mac screen?
Apple's mandated solution would be to wait for the photos to upload to your Photo Stream or iCloud Photo Library, then start a slideshow in iPhoto or Aperture.

Alternatively, you could make your Mac into an AirPlay receiver using a 3rd party app such as AirSquirrel's Reflector. This one is paid, but I'm not aware of any free equivalent.