The bluetooth speaker is designed for newer, much larger phones, so I had to make a bracket for it first. The design (in OpenSCAD) and STL files are on Thingiverse here - iPhone 5 bracket for PTH800 Bluetooth Peterhot Retro TV. I printed the bracket in orange to make the speaker. The bracket also includes voids for two button inserts so that the volume up/down buttons can be accessed.
The fit was quite good, can't say as much for the condition of the iPhone back and camera though!
All put together it looked like it was meant to be like that from the start!
The only other thing that I needed was a way to charge both the iPhone and the Bluetooth speaker at the same time, so I used a 3-in-1 cable (similar to this one).
This works well for playing music (especially if you have Spotify and can play on other device) and watching YouTube. The screen is a little small though, but at least this way the phone is put to some use and not just thrown out.