Where are imported songs stored on iPhone?

In Refrain's own document directory on the device. Importing copies the file rather than pointing at where it came from, so the audio and artwork are real files on the phone, and a small local database holds the metadata, playlists, play counts and your edits.

That copy is why offline playback is dependable — nothing can move or un-share underneath it — and it is why deleting the app deletes your library.

Delete vs Offload

An important distinction in iOS:

• Offload App removes the app binary and keeps its data. Reinstall and the library comes back. This is the safe one, and it is what iOS's "offload unused apps" setting does.
• Delete App removes both. The library is gone, and there is nothing on our end to restore from, because we hold nothing.

No app on iOS can leave files behind when deleted. This is not Refrain being careless.

Is it in my backup?

Yes, if your backups include app data.

An encrypted local backup to a Mac or PC includes the app's documents, so the library restores with the phone. iCloud Backup does too, though a music library will consume your iCloud allowance quickly — a few hundred songs is several gigabytes.

Neither is a substitute for keeping the originals, because a backup restores to a phone. It is not a folder you can open or hand to someone.

How much space is it using?

Settings → General → iPhone Storage → Refrain. Almost all of it is audio.

Per four-minute track: MP3 5–10 MB, FLAC 20–30 MB, WAV about 40 MB. To reclaim space, delete individual songs rather than the app.

Getting files back off

Refrain moves files one way — computer to phone. There is no export.

You can reach the app's documents through Finder's file-sharing panel with the phone plugged in. That works, and it is not a plan.

The plan is to keep the originals somewhere that is not the phone: a Mac, an external drive, a cloud folder. Then the phone library is a convenience you can lose rather than the only copy.

Related

• Where your music actually lives, and what happens when you delete the app
• Four ways to get music into Refrain
• Privacy