Place all of the theme graphics in your title in the desktop view. Then move the graphics intended for phone and/or tablet off the page.
In phone view, move/size the appropriate graphics on the page and the desktop graphics off the page.
We do something similar with a simple text box instructing students that the course is best viewed in landscape and please rotate your device. This text box is off the page in desktop and landscape views. We move it onto the page in portrait views and size it to fill the page so this message is the only visible object.