If you stored your GarageBand Songs in iCloud, they have not been included in the iCloud backup of your iPhone.
To access them again, ensure, that iCloud for GarageBand is still enabled.
See this Help page: http://help.apple.com/garageband/iphone/2.0/index.html#chsdfe5c2c2
You turn on iCloud for GarageBand in the Settings app on your device.
- Close GarageBand.
- On the Home screen, tap Settings, then tap General.
- Tap GarageBand.You might have to scroll down to see the GarageBand icon.
- If the Use iCloud switch is not turned on, tap it.
Now the GarageBand songs should appear again the My Songs Browser:
In the My Songs browser, songs available to download appear with a download badge.
Tap a song with a download badge.
If there is a newer version of a song on iCloud, the newer version is downloaded to your device. If the version on your device is newer, the newer version is uploaded to iCloud.