How can I get rid of multiple “purchased on ” playlists? When I got my first iPhone and bought something via the iTunes app, I got a playlist in the iTunes source list underneath the “Store” heading for all the songs I purchased on the iPhone.

I’ve had a few more iPhones since then, and each phone has also been given its own “Purchased on” playlist in iTunes. They’re now taking up quite a lot of space in the iTunes menu.

Is there any way I can consolidate, or just get rid of, these playlists?
You can't consolidate them, but you can delete them. Just right click and click "Delete".