Hi MDTerp,
It sounds like you are wanting to transfer your audiobooks from OverDrive to iTunes so you can import them to your iPhone. We can help get you pointed in the right direction for support with this.
Depending on which model of iPhone you are using, you may be able to download the OverDrive application on your iPhone and access all your audiobooks without having to sync with iTunes. You can find more information about the application in the App Store here: OverDrive: eBooks & audiobooks
If you would prefer to use iTunes, you can find out more information about importing media into iTunes here: Import media from a computer to iTunes on PC
Should you need further assistance with the OverDrive files, we'd recommend contacting them directly for assistance.
Take care.