People "overthink" the cable you need.. mine is really easy & out of the junk box
The problem is that, with the Chinese radios, the PTT is activated by shorting the speaker ground to the mic ground, so ANY common ground will make it transmit..
So... I simply put an audio transformer in the mic cable... So it the cable is "straight through" for the audio OUT of the radio, but both wires from the Mic connector for the radio go to one side of the audio transformer, and the continue from the other side to the device.. thus no common earth!
I know purists will hate this, as the impedance will be all over the place, but essentially you just have to have the "volume" of the device up loud enough to just trigger the VOX ( which will be LOUD for various reasons!!)
Audio transformers are usually only a couple of dollars to buy, but if you have an old transistor radio around
You can probably put the transformer in the speaker lead instead, but I think a phone etc. will be more "forgiving" of the impedance weirdness
*** IMPORTANT*** anyone who does this, ensure you monitor your transmissions when you do this to ensure you are not making a really BAD noise on the APRS frequency whilst you get it going Your mileage may vary!