https://thenextweb.com/gadgets/2018/07/27/amazon-alexa-now-lets-you-control-music-from-your-phone-on-echo-speakers-chromecast-style/

Your Amazon Echo speaker can play music on demand, provided you ask it to do so with your voice or switch to Bluetooth mode. Now, you can use your phone to control playback, just like you would with a Chromecast-equipped device – no Bluetooth required.

Essentially, Amazon has updated with its AI assistant with a feature called Alexa Cast. It’s presently only available in the Amazon Music app, so you’ll need to use that if you want to launch playlists, skip songs, and play or pause without having to yell at your speaker.