You need to go into the Music settings on your phone and make sure that at least "Connect with Xbox Music" is On.
The other thing I found long ago with Microsoft is that you need the "Artist Album" tag filled appropriately. Just the "Artist" tag isn't enough. Why Microsoft does it that way? I have no clue.
Another thing you can do, is on your computer you can use either Media Player, Media Center, or Zune and have it updated all your tags for you from Microsoft's databases by going in the Options, Library settings and enable "Retrieve additional information from the internet" and select either options (Add missing or overwrite all). After you either manually or automatically updated the meta info, recopy your music to your phone.
SUGGESTION: Make a backup of all your music first!!!!! You may not like how it turns out.