transfer all songs to mac from iphone and then putting it all back

hi to the people that can see this...

I got a iphone 5 from my brother and we want to transfer all his songs onto my mac and then deleting them on the phone. However, we had an agreement that in the future if one day he needs his phone back, he also wants his all his songs back with it. We want to find out away to do that. Is it possible?