Visiting twentyfourteendemo.wordpress.com with a smartphone results in the same: the featured posts show with their image, non-featured posts show with a thumbnail.
When I use twenty fourteen without featured posts and without images, the smartphone view will only show the post title (and date & author).
I have experimented with a child theme and variations of the media queries in style.css, but it didn't work. I had to modify the original style.css too, to get the desired result.
Any idea to fix it in the child themes style.css?