Best answer by Mathis
Thank you for posting on the forum. I've looked into this for you and I believe I can tell what seems to be the problem - the way the original file was recorded (probably mono) causes for the channels to be muted when listened to on the iPhone (where the mono signal gets split and the split channels cancel each other's audio basically. The keyterm here is "phase cancellation").
Now, how can you fix this? I'd recommend for you to use an audio editor like Audacity to create a native stereo file out of the recording, then upload it again (you can export the file to a stereo file once imported).
It is not something that occurs very often, but also, it sounds more complicated then it is, really.
Can you give this a try and let us know if you need further assistance? We can then take another look together, no problem :-)