I have an S6 and it has a star to tap for favorite, the SWMBO has got an A5 and try as I could I could find no way to add a favorite, I got round this by opening contacts, then hitting edit, hitting "Groups" then adding "Starred in Android" when I got back to contacts the numbers were in a group under Favorites.
Why oh why when it was simple to hit the favorite star do I have to run rings around the damm OS to get working something that was working before.............