Mobile phone amplifier

As my mobile phone's speaker is on the side, I've open a slot to allow the reverberation of the sound against the back of the amplifier.
As the original file from @edditive was available only in STL, I've redesigned it from scratch.
It works for a mobile phone up to 11.5mm thickness.

Video with sound to be able to compare is here: https://youtu.be/txrX90mA7qI

Thanks to @edditive for the original design.