Output Macbook audio to iPhone or iPad
I'm wouldn't be so sure there are better alternatives. AirFoil is still updated regularly, and as its a rather rare need to stream from a computer to an iDevice (and not an AppleTV, HomePod, Miracast, Chromecast, Bluetooth speakers), it's a safe a reliable bet. You could also take a look at the AirSquirrels programs, (Reflector, AirParrot, etc.), but I'm not sure they actually do what you want precisely.