Deleting photos from iPhone which are already synced with my Mac How do I delete synced photos from my iPhone when the same photos are already deleted from my iMac and also the trash?
Normally, if photos are synced through iTunes to an iPhone from a Mac folder, iTunes should automatically take care of removing photos.

If that doesn't work, try to disable photo syncing first (uncheck "Sync Photos" in the iTunes-->iPhone-->Photos tab), sync the iPhone once, then turn on photo syncing again (by checking "Sync Photos").