Audio amplifier kills FM radios signal
Well at first you should never connect earphone output to the phono input of any amp.
You will overload the amps preamp stage which at least would cause you distortion or worst blow the amp.
I just looked at the amp its got a mp3 input: try that.
The problem you got, is that it does use the earphones has a aerial so only thing I can think of is to strip some of the plastic of to expose the shielding plus it depends on the length of the wire, all a pain. I would go out and buy another radio.