Songs from iPhone won't transfer to iTunes on my PC
You can't transfer music from iPhone to iTunes. You can only transfer music iTunes to iPhone. This is to prevent music from being pirated easily.

If you purchased the music directly from iTunes, all you need to do is make certain that you have iTunes signed on to the same Apple ID and download your purchases directly. You won't be charged if you already purchased via your iPhone. In iTunes go to Store > Check for available downloads.