Sibilance on cell phone

Yes, that is indeed what I was wondering... what are the peak levels on the file you were exporting? One thing that can really screw up MP3 exports is having the level too high when they're encoded. You really don't want the peak levels to be any higher than about -2dB tops if you don't want to run into problems with them. The other thing that might help is to run a limiter on the peaks before you encode it. This will let you bring the overall level up slightly and stop any nasty peaks occurring. If you use Effects>Amplitude and Compression>Dynamics Processor and look for the Vocal Limiter preset, that will give you a reasonable starting point. If you're going to use it though, then normalize all the audio to 0dB before you use it - that's the level at which it's designed to work.