Product Demo Audio Not Playing on iPhone speaker via YouTube?

I created my first multi-cam prodect demo and everything sounds great in my project and in the exported file. The issue comes, when you try to listen to the video on YouTube via the iPhone (speakers). The intro music sounds fine but the dialogue is very extremely low with lots of static. I recorded the product demo with a DSLR via a Lavalier mic connected directly into the camera. When I brought that footage into FCPX, the audio came in as 2ch Stereo. Now that I created the multi-cam, not sure whether I should adjust the audio in the original clip/multi-cam clip or directly in the project that i cut. If I adjust in the original clip, will it trickle down to the Multi-cam clip I created. Someone mentioned adding a "Gain" effect, selecting "convert to mono" and choosing either phase left or right. That didn't seem to work for me either. I am at a loss.

Below is the video in question.


Sorry and thanks, in advance for the newbie question.