iTunes Match will replace the music library on this device?

I signed up for iTunes Match on my computer iTunes account. I noticed that 3/4 of my library was missing and that most of it is on my iphone. When the backup to the iCloud Match account was completed, I went to enable itunes Match on my iphone and it asked me "iTunes Match will replace the music libary on this device. 'Enable?' and I declined... but how do I get my music on to my computer again!?