IPhone – two itunes libraries – one on external hard disk

Two software options (for both Mac and Windows). Both turn your work computer into an Airplay destination, so you can stream audio directly from your iPhone to your computer. This lets you play music from your iPhone without worrying about syncing, copying songs, etc.

On the Mac, there's the open source app called Airmac. And on Windows, you can try the application Shairport. Both do the same thing, and turn your computer into an Airplay destination.

Once you have turned on one of these apps, start playing a song from your iPhone. If everything is on the same network, you should see the Airplay icon (shown here in the lower right, the rectangle + triangle). Tap that, you should see your computer listed, tap that, and then your phone will stream the iTunes audio to your computer.

Hold down the Option key when you launch iTunes. You will be asked to choose an existing library, or create a new library. You can search the web for iTunes multiple libraries and find the answer.

I suggest that you create a new iTunes library, move songs that you don't listen on a regular basis over there. If you already have them in a play list, just export them from your primary library and import in the other library.