If your 1024 x 768 layouts are using PDF background as the format, there
isn't much reason to produce a 2048 x 1536 edition as all vectors and
type will scale nicely. We do not have support for multiple content
files per article record, though that is something we are evaluating
(Remember we're still in beta). If you wanted to display a different
article for the phone you would create a new article to contain the
phone content files and then place it in the default collection for
phone content.