Yes...using the standard Player component running a normal UI/foreground process, I have used the PhoneActivity component to detect phone call start/end. It works, but within the event, the player dies not respond to Player.Start to continue playing - instead it remains paused until the call ends.
Seeing what @Taifun has provided explains it...what I want is mute instead of pause, which seems to be in keeping with the idea behind the phone call priority ... be nice if there were an option to select whether to pause or mute other audio (or a particluar app's audio) during a call.
For my application, if I am unable to somehow substitute mute for pause, I can use the PhoneActivity or, in the case of the AudioExoPlayer, the focuschange event to capture the delay being currently applied to the active live stream and then have the end of the call (or restored focus) event to restart the player with the recorded delay...but it would likely add additional delay - but maybe not enough to matter???
However, as I mentioned in an earlier message, the Player in my app runs in an Itoo process and so I must now test your AudioExoPlayer.FocusChanged event to see if it works there 
.... PhoneActivity does not work with the current version of Itoo (Open Source • Background Tasks: Itoo 
- #1165 by Randal_Andress)
If your AudioExoPlayer.FocusChanged event works from an Itoo process/service, then I may have my solution.
Thanks, and I'll get back to let you know whether or not it works for me.
Kind regards,
Randal