Thanks for the reply.
I can resize the crop box but it only resizes proportionately, and maintains its square ratio. Since images I have are full screen, and the screen is noticeably rectangular, the crop box will only enlarge until the edges have reached the narrower dimension of the image (horizontal). The crop box stops enlarging because, if it were to elongate vertically, that would not keep the box a true square.
Maybe the images I download need to be more square-ish and not rectangular like the physical screen of the phone?