how do you delete photos from the photo stream on the i phone

You can look this up yourself. Type "photo stream" into the search bar at the top of this page.

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How do I delete photos from my Photo Stream?

You can delete photos from your Photo Stream the same way you delete other photos from your device. Just select the photo you want to remove and tap or click Delete. When you delete a photo from Photo Stream on one device, iCloud will automatically delete it from the Photo Stream album or view on your other devices.

Note: Deleting individual photos from Photo Stream is supported by iOS 5.1 or later, iPhoto 9.2.2 or later, Aperture 3.2.3 or later, and Apple TV Software Update 5.0 or later. You will need to manually delete photos you downloaded to iOS devices running iOS 5.0.1 or earlier after updating to iOS 5.1."

iCloud: Photo Stream FAQ

Not true in deleting photos automatically from photo stream. I deleted photos from phone and they showed up when trying to choose existing photos at Facebook. They are gone from phone but not photo stream. BEWARE . You can turn off photo stream in settings on your iPhone.