How can I get songs that are on my iphone on to my itunes.?

I have a Mac and I emptied my trash yesterday. I saw that there were audio files in there and at first i took them out but it wouldn't let me drop them into itunes. now it says that my songs "can not be found" and i have still synced my phone and the songs remain on there. I am only worried because i think i will lose the songs if i get a new phone which will happen eventually. is there anyway to get the songs off of my phone? please help me!!!