Deleting music to free up space

[ALindquist5]

Most of my Spotify playlists are a combination of imported music I had in iTunes and songs I've added since getting Spotify Premium.  My iPhone storage is limited, though, so I'm looking to free up space.  If all that music has already been imported into Spotify from iTunes, can I go into iTunes and delete playlists and music files to free up space without wiping the music out of Spotify?  Are they duplicates or are the iTunes files required and linked to my Spotify songs?

[Joe]

You can delete any original tracks from your phone safely as spotify has its own method of adding music to a mobile device and doesn't need to access mp3s, m4as etc on the mobile.

[rebekahlynn06]

My offline sync also doesn't work. Haven't found any answers. I'm connected to wireless & my phone is plugged into my computer. I click the button "available offline", it goes green, nothing else happens. any ideas??

[Peter__]

Do you have at least 1GB+ of free storage space on your device?