Recorded song in GarageBand and uploaded to iCloud but file now missing from phone
I found some instructions that might help you with your problem.


  When you want to send a song to iCloud, tap on the Edit button and
  select a song (or songs). With iCloud enabled in the app, you will now
  see an iCloud icon along the top bar. Tapping on the iCloud icon will
  bring up a prompt, asking if you want to send the song(s) to iCloud.
  
  After the song is uploaded to iCloud, you will see an iCloud logo in
  the top-right corner of the song thumbnail, indicating a successful
  upload and the fact that the song is stored in the cloud.