You can manually manage the contents between your devices and your computer. When you manage the transfer of contents between them, you can set the device not to automatically sync thus could make sure not automatically delete the contents that are in your iOS devices and replace them with the music you have in your itunes.
The more detailed instructions on how to configure your devices for manualy management can be found in the article that follows:
Managing content manually on iPhone, iPad, and iPod
I hope this works for you. Happy New Year!
It is on iTunes but once I unplug the phone the playlist goes away
If that is the case, something in the sync is not working properly.
Is the content actually selected to sync?
Is it merely the playlist that is "disappearing" or the content in the playlist? They are two different things.
It may be necessary to remove all media from the device then sync back what is desired to correct the issue that is occurring.