Quite the apparatus he devised - I think it was a joke - at least the writing under the video indicated that.
Anyway we got the project done. A little background. The front part of my shop is under the deck at the rear of our house and two weeks ago I had the decking replaced (5/8 ply) as it was old and starting to delaminate. In the process as I was moving some things on the uncovered deck I fell through a gap and did a number on my left leg. I've been limping around like a one legged pirate since.
Due to the deck repairs, the front part of the shop now has insulation hanging down from the ceiling - I was planning to put it up properly but that hasn't happened as I don't really feel like climbing around on ladders at the moment. My shop is so cluttered I have to take things outside (in the snow and about 0 C weather) if I want to use my planer and table saw. So as you can imaging it was a real comedy of errors making this "amplifier".
We did get it done:
You will likely notice the small cross piece anchored by two brass pins - that was to cover up a mistake. I find in (my) woodworking that being able to make mistakes look like features is very valuable.
The spacers (all along the edge) in this design are about 5/8 in. square section and the front and back pieces are 1/2 in. thick. It seems to me that using spacers that were very thin (eg. 3/16 in wide x 5/8 in thick) and using a thin front and back might make this design resonate and work better. I'm no acoustic engineer so this is just a guess. My changes would make it more like a stringed instrument box. I suspect that making the box bigger would also help.
The box does work moderately well. It gives the phone a deeper sound and does amplify it a bit so in that regards it was a success.