When i click on trash can to delete selected photos the trash can is grayed out and will not delete photos

That normally means the photos you are trying to delete, were synced to the iPhone from a computer.

As such, the only way to remove them, is to unsync them by deselecting them in iTunes / Finder or selecting an empty folder / album.

Sync your photos manually using the Finder - Apple Support

If the trashcan icon is disabled it means the Photos were synced from a computer to the iPhone.

You need to unsync them the same way to remove them.