First you will have to address the reason for the iPhone not appearing in the side bar.
One assumes, possibly incorrectly, that you do actually have a side bar visible in iTunes 11. The reason I mention that is because the side bar is not visible by default in the new version.
To make it appear, launch iTunes and go to the Menu Bar, where it says File, Edit, View, etc.
Choose edit and select Show Sidebar.
Now can you see your iPhone?
Now the next problem. The playlist, "Recently Added", is it one created by you or one of the built-in ones?
If it is a built in one, then the only tracks that are in there will be the ones that are "recently add", as the name suggests.
If you created it, then it could have ALL your tracks in it.
Suggestion: Create a Playlist specifically for your iPhone. Drag everything you want on the iPhone, into it. Connect the iPhone, and set the Preferences so that iTunes only Syncs that one specific Playlist.
Then do a Sync.
Not only does this backup your iPhone, in the case of an iPhone failure or software glitch, it does not remove anything from the iPhone and copies any track or app that you have purchased via the iPhone, in to iTunes.
Only items that are in that Playlist are moved to the iPhone.
I'm having troubles putting new music onto my iPhone via the way I used to do it on the old iTunes. I used to drag my 'recently added' playlist straight onto the iPhone in the side menu. Now the iPhone doesn't appear in the side menu, and it doesn't appear to be able to receive this playlist via the dragging method I adopt. I know I can choose to sync it, but this will wipe all previously added songs and just have the 'recently added' playlist in my itunes. Does anyone know how I can get my recently added playlist into the iPhone while adding to all previously added songs?