The device you've linked to, Bobbi, is basically the same as the one I linked to before. Both will work but, in either case, you need to remember that they need a power source. They get that power through a 5V USB lead, so you'll need to have a USB socket available to plug the lead into.
Once you've got the device powered up, and the audio from your iPhone feeding into it via Bluetooth, you can simply connect an RCA stereo lead between the adapter and the amplifier. (That, of course, assumes that the amplifier actually has RCA phono sockets available for its input source. Apart from its power output, you've not provided any information about the amplifier up until now).