I designed this with the intention of printing it in Wood PLA from the beginning. This meant that I could get away with high layer heights to mimic wood grain. I also used a fair amount of infill to add weight to it and depth of sound. I only tested this with a few cellphones that my friends and family had available. It obviously won't do much if the audio doesn't come out the bottom of the phone.

I initially posted this over on imgur as I had no intention of putting the design up here, but at least one person asked for the stl so I'm getting over my self conscious nature and putting here for anyone to print.
I know it's not perfect and I've tweaked it a bunch of times already, but it works mostly, save a few issues with using a charging cable.
If you do print this, I would sincerely love to see your makes.
If you remix this, please let me know so I can get better at this stuff, I'd love to know how you came up with whatever tweak you might do.