Solution for somewhat unique situation?

I?m not 100% sure if this is the kind of question that?s appropriate for this forum, but I honestly am not sure where else to ask. I have a very specific need I?m trying to fill, and I?m trying to figure out what combination of cables and adapters I need to make it happen.

I coach track at my school, and I use an iPhone app (SprintTimer) to time my home meets. It has a feature that can use sound to trigger the start of the clock. What I would like to do is utilize a pair of two-way radios to carry the sound from the official’s starting pistol to my iPhone. To do this, I need to connect the headset output of a two-way radio (most likely a Motorola T200) to my iPhone XS. I have the lightning to 3.5mm adapter that came with the phone. What I need are any appropriate cables and adapters to get the audio output from the radio to the input of the iPhone 3.5mm to lightning adapter cable. That way, the official can hold one radio, and press the transmit button when he fires his pistol. The sound from the gun would be received by the other radio and transmitted to the iPhone via the headset jack which would trigger the start of the clock.

I’ve tried looking into what kind of cables I’d need, but I can’t find any definite answers. I know enough about audio cables to know there are enough different kinds (TRS, TRRS, etc…) that simply buying the first one I found might not be the best idea. I was hoping someone here might be able to point me in the right direction.

Thanks in advance to anyone who is able to help me out with this.