Here's a suggestion, instead of trying to get all of your music on your phone, why not just set up a smart playlist and have it put some of your music on your phone. Then each time you sync your phone to iTunes, it will swap out the recently played songs for song you haven't heard. This is what I do with mine because I have a vast collection of music that won't all fit on my phone and I have 32 GB on my phone! Here's my smart playlist:
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