I've been trying to resolve this for a week or so. Specifically, go to the top right, Menu, (that used to show 5 or 6 items) and pick Add contact to home screen. Done. It was that easy.
I discovered display S6s in a store would do it, but the salesman's and mine would not. Marshmallow was the answer - I think.
Why the need for this? Well, sometimes I use it for perhaps an hour or so, then bin it. I don't want to mess with several moves to Widgets just for that. I loaded one of the suggested Apps - Speed Dial by Codificator - and it's very fast. Thanks for the suggestion.