That is a very interesting & useful idea.

It would seem the two main issues would be:
1. Delay
2. Equalization

They may be concentrating on a best result for a rather basic non-application based system, like the systems now used in drive-in movies: just tune your radio to a stated frequency & receive audio - in this case, audio that has been emphasized at the mid to higher frequencies.

If they wanted to get fancier, they could create an application for the project, & do things like send timecode information over the FM subcarrier so that the phone could adjust the delay based on its own clock.

Alternatively, they could use a proprietary audio transmission format over wifi which includes timecode and equalization benchmarks as well as the digitally-encoded audio. Calibration of EQ for the position of the phone in the venue might be done by first a chirp of pink noise from the phone when the application is started, the microphone establishes that chirp for the base frequency response of the speakers, and then occasionally compares microphone samples of concert audio to a transmitted expectation of frequency response to adjust EQ on the phone's speakers.