On my iPhone 7, I go and open up photos, then click on "select" photos. I then select a photo. There used to be a "Add to" button in the middle of the bottom (to the left is "upload" and to the right the "trash" button).
The "add to" (which allowed me to send the photo to another folder) is no longer there. Disappeared.
Hope that explains it better.
How do I add this photos to other albums?