Syncing my iPhone..

So most of the time I buy my songs on my phone.. I havent hooked up my phone to the computer in a long time. When I go to click sync music, the playlists that are normally on there are gone and im scared of losing all my music. Is there anyway it wont do this or can I get the music on my phone to a disk? please help asap.. my phone is broke and wont last long :(