Is it possible at all to airplay audio from an iPhone to a MacBook Pro? that is play from iPhone but select the output to be the MBP speakers instead of the airPods or internal speaker of the phone.
Are you asking about a native way to do this from macOS, or with third party apps?
As far as I know there is no way to arbitrarily play AirPlay audio to macOS, but your macOS devices can show up as recipients for some things like phone calls (by selecting the speaker button during a call).
On the third party side of things, there are a couple of apps for macOS that claim to allow this (I have not tested any of these personally). Check out AirServer and Reflector. From their website, AirServer seems to have a lot of features, and compatibility for more than just AirPlay. AirServer has a trial and a discount for students, so that's where I would start if I were in need. Additionally, I couldn't find if Reflector supports streaming just audio, but AirServer supports lossless audio AirPlay playback.