Deleting Photos on iPhone - From Photos > Collections

Hi,

I hav done a reasonable amount of reading both on and off Apple support and can not find a solution.

I have an iPhone 5s running iOS9. I would like to delete photos that appear under > Photos (Photos home screen icon) > Photos which then displays Collections (by year and date).

Problem is: When the "Select" option (top righthand corner) is selected and a photo selected the "Trash" symbol is greyed out! So I can not delete them from iPhone.

The photos are location and date ordered and appear on my MAC, so I don't want them on my iPhone . I've considered syncing and then de-syncing BUT, the particular location and date "folder" does not appear in the Sync area in iTunes. Secondly, any location or date folder that does appear in the Sync section of iTunes does not appear on my iPhone (which is what I would like) - If that all makes sense.

Is there an easy solution to be able to delete these photos of iPhone??

Regards

Ash767