https://www.theverge.com/2018/7/26/17616510/amazon-alexa-cast-announced-music-playback-control

Amazon is introducing a new feature today called Alexa Cast, which lets users control what’s playing on their Alexa-enabled devices from their phone. At launch, its abilities are very limited: it only works with the Amazon Music app to control music playback. But it’s easy to imagine this becoming a full-on competitor to the very-similarly named Google Cast, eventually allowing you to control playback of music, movies, podcasts, and more from any app that wants to specifically support Amazon’s network of devices.

Alexa Cast works with any Alexa-enabled device, so it supports Echo speakers, third-party Alexa products, and some of Amazon’s Fire devices. After an update today, the Amazon Music app on iOS and Android will include an icon for Alexa Cast on the Now Playing screen. You’ll be able to tap that to get a list of all of your Alexa-enabled devices and select which one to start playing music on. The app will stay in sync with what’s playing on the speakers, so you can continue to control music remotely or switch to playback on your phone if you leave home.