If you watch the video you will see that this is a passive amplifier for the iPhone.A sound channel from the speaker on the bottom of the iPhone runs to the speaker hole. This gives you about a 50 % boost in volume and slightly better base.
The next picture shows the pieces before glue up. the second from the bottom shows the sound channel. I use a large forstner bit to drill the hole after everything is glued together.These bits are expensive so if you don't already have one you will need to use the scroll saw to cut the holes before glue up. In that case add a 1/4" thick piece to the back that does not have a hole. Cut a 2.75 inch hole in all the other pieces.
If you want to watch the video I recommend watching it now. Youtube has a habit of taking down videos with music in them. This one might not stay up long.