Use iCloud with GarageBand for iPhone
You can upload your GarageBand songs to iCloud Drive and access them from another app or other devices. You can open your songs directly from iCloud Drive in the sidebar in the My Songs browser, or download them to your iPhone.
When you close a song or close GarageBand, the song is updated with your latest changes in iCloud. If changes made on multiple devices are out of sync, a copy of the song with the newest changes is saved to the same location as the original in iCloud Drive.
Before you can use iCloud Drive with GarageBand, you must set up iCloud in the Settings app on your iPhone. More information is available online at the iCloud Support website.
Turn on iCloud for GarageBand
You turn on iCloud for GarageBand in the Settings app on your iPhone.
Close GarageBand.
On the Home screen, tap Settings, then tap your name at the top of Settings.
Tap iCloud, then tap the switch next to GarageBand in the list of iCloud apps.
You might have to scroll down to see the GarageBand icon.
Upload a song to iCloud Drive
In the My Songs browser, tap Select.
Tap the song you want to upload, then tap the Move button
.Locate where you want to save your song on iCloud Drive, then tap Copy.
Copy a song in iCloud Drive to your iPhone
In the My Songs browser, tap iCloud Drive in the sidebar and locate the song you want to copy.
Tap Select, tap the song you want to copy, then tap the Move button
.Locate where you want to save your song on your iPhone and tap Copy.
Open a song in iCloud Drive
Songs available to download from iCloud Drive appear with an iCloud download badge 
.
In the My Songs browser, tap iCloud Drive in the sidebar, then locate and tap the GarageBand song you want to open.
The song is downloaded. If there is a newer version in iCloud, the newer version is downloaded to your iPhone. If the version on your iPhone is newer, that version is uploaded to iCloud.
Create a song in iCloud Drive
In the My Songs browser, tap iCloud Drive in the sidebar, locate and tap the GarageBand for iOS folder, then do one of the following:
Tap the Add Song button
at the top right of the screen.Tap Create Document in the My Songs browser.
The Sound browser opens, where you can choose a Touch Instrument to use in the song. When you close the song, the latest changes are saved to the original location in iCloud Drive.
Delete a song in iCloud Drive
When you delete a song in iCloud Drive, the song is deleted on all your devices.
In the My Songs browser, tap iCloud Drive in the sidebar, then locate the song you want to delete.
Tap Select, tap the song you want to delete, then tap the Trash button
.
If you turn off iCloud for GarageBand, your songs stored in iCloud Drive will be deleted from your iPhone, but will remain stored in iCloud Drive. If you want to turn off iCloud and keep your songs on your iPhone, you need to duplicate the songs you want to keep before you turn off iCloud.