How do I get the Plex app to use synced content over streaming?

I have used mobile sync to upload all of my music to my iPhone 6. I have Plex app ver. 4.4 and have Prefer Synced Content turned on under Advanced settings. Unfortunately the app is still streaming my files. It was my understanding that with this option turned on my files would play locally without having to switch my server to the local iPhone. If that is not the case I am a bit miffed as to what that setting is used for.
I have also tested this on the most recent Beta (sorry I don't remember the version) and the files are still streaming.