Add in resistance to the line between the amp and earphone is like raising the resistance if your earphone, and it makes your amp happier. Usually adding impedance to an earphone is a good thing and makes amps happier. Others here can get into very technical discussions about impedance matching. But that's the gist of it.
Sorry to say, I think you got this wrong. Adding a serial resistor is not raising the impedance of your phone. Please google for "headphone impedance explained".
Edited by james444 - 5/16/13 at 2:58pm