Photos can't be deleted from iPhone
If the photos were put by syncing with iTunes you can't delete them using iPhone.

To delete photos and/or albums that were copied to your iPhone by syncing with your computer are deleted by doing another sync. 


Start iTunes on the computer and connect your phone.
Select your phone in iTunes and select the Photos tab. 
Then DESELECT the items you no long want on the Phone. 
Then click on Apply or sync. 


The photos or albums will be removed from your iPhone but they will remain on your computer.