How to save songs from my iPhone if I sync to my computer?

Okay, I have several albums on my iPhone 4s that I do not have in my itunes library, nor do I have them on a cd to transfer to itunes, and I also have songs in my itunes library that I want on my iPhone. If I want to get the music onto my phone from itunes, I have to sync, but if I sync, it will erase all of my music on my iPhone and I will lose all the music I want to keep. A lot of the music I have on my iPhone that I want to keep is by bands who aren't that well known and do not have their music on iTunes… What do I do?

Follow the steps:

1. Download and install some iPhone manager.
2. Connect you iphone with pc.
2. With this iphone transfer, transfer songs you want to keep from iphone to pc.
4. Transfer songs from pc to iTunes, then sync your iPhone with iTunes.

If you have not used any iphone manager, try this free one: Syncios
Refer to this tutorial:
http://www.syncios.com/how-to-transfer-music-from-iphone-4s-to-computer.html