I have a Liberty 4500 portable PA system and a headset plug to male XLR adapter.
I am afraid the phantom power from the Liberty PA system will fry my iPod.
How can I prevent it from happening?
It looks like the Liberty 4500 has two XLRs with Phantom power and one 1/4" line in.
The 1/4" line in is the one you want to use for the iPod, as it does not have phantom power.
You will need a cable with a 3.5mm stereo male connector on one end and a 1/4" mono male connector on the other. The closest I could find were a 3.5mm stereo male to two male RCA connectors cable and a two female RCA to 1/4" mono male adapter.
You'll probably want to use the 1/4" input, because it won't have phantom power.
An adapter from iPod (or other 3.5mm device: smartphone, CD player, computer…) to 1/4" will run you about $4.
If you have the manual for the Liberty 4500 (I can't find one on Google), see if it supports disabling phantom power on one or all of the XLR inputs.