Why do the songs on my iPhone get erased every time I try to sync it?

Every time I want to add a new ringtone, episode of a show, or movie, I get warned that all of my existing songs on my iPhone will be deleted. I get tired of having to refill all my songs everytime I want to add something new from my iTunes. Why does it do that and is there a way I can disable it or something?

Because your iPhone and iTunes is set as "automatically sync music and songs" or something like that. So when you sync it will erase music from iPhone that's not in your iTunes library. You will have to connect your iPhone and click on it on iTunes then find where it says "automatically sync music or song" and uncheck it. Sync and then resync to get your music back. Hope that makes sense