Q: airplay INPUT on iMac?

I'm running 10.11.1 although I suspect this question applies to several of the last OS X iterations:

For several reasons I'd like my iMac to sometimes present sound on whatever is playing on my iPhone through AirPlay. If this were possible, I would expect the iMac to appear as an AirPlay option on the iPhone and  I'd expect an option in Sound/Input similar to Sound/Output. But perhaps there's another setting?