Getting Audio In and Out of a Mobile Phone
I've seen this come up in several different situations so I thought it would be worth creating a new post. When you need to get audio in and out of a mobile phone that has a 3.5mm headphone jack it's important to know that there are two standards for the wiring of these jacks. Using the wrong adapter can cause all sorts of "weird problems" or it simply won't work depeneding on the phone.
One standard is AHJ or CTIA and the other is OMTP. While both use a same TRRS plug, the American Headset Jack or Cellular Telecommunications Industry Association standard defines the wiring differently than the Open Mobile Terminal Platform.
For AHJ/CTIA the Tip = Audio Left Out, the First Ring = Audio Right Out, the Second Ring = Ground, and the Sleeve = Microphone In
For the OMTP standard the Ground and Microphone In are swapped. In other words, T = Audio Left Out, the first Ring = Audio Right Out, the Second Right = Microphone In, and the Sleeve = Ground.
This same information applies to the 3.5mm jack on a Lightning Audio adapter or a USB-C Audio adapter.
Again, make sure you are using the right splitter adapter that matches your phone jack.