In general, to stream audio from your iPhone to an AirPlay speaker you’ll need to locate the AirPlay devices menu within whichever media player you are using. To AirPlay audio from Spotify to a speaker, click on the media player within the Spotify app, click the speaker icon in the bottom left corner, and select Apple AirPlay. From this AirPlay menu you’ll see the names of all your compatible speakers. Similarly, to stream YouTube, click the icon at the top of the video player that looks like a rectangle with a tilted WiFi symbol in it, and then select AirPlay devices.