Deleting music on Spotify

[lsarocker]

Hi there, I have 2 iphone 4s devices, my idea was to use one just for Spotify music and the other as a general smartphone so that one phone does not get all the memory used up for music tracks. However I see the music I have downloaded to listen to offline is duplicated on both phones. Can I delete Spotify on one phone but leave it on the other? Sorry if this seems basic and obvious but I'm only just starting to get the hang of Spotify premium, which so far I must add is brilliant, I've got loads of music I can listen to offline anywhere at great quality with my JBL speaker. Cheers allan.