The main issue here is usually that the microphone connector on your handset is used to work with much much lower signal levels.
In best case it could help to reduce the volume on the soundcard output (line-out) to a much lower level by lowering the output volume to a minimal level. However also the impedance is different and might require some adaptation.
The circuit needed to connect a line-out to an e72 might also depend on the type of mic supported by the phone. I found some basic information here here.
What puzzles me a bit is why you want to do such a thing. The e72 seems to be able to play digital audio files directly (transferred via memory card, bluetooth or cable I guess). So it might be much easier to record on your PC and then convert to any suitable digital format for transfer. There should be some software included with the device already. For audio manipulation I can recommend using Audacity.