I do something similar but with an Amazon Echo Dot with the microphone off instead of a phone. It shows up as an available Spotify Connect device on my computer

I do something similar but with an Amazon Echo Dot with the microphone off instead of a phone. It shows up as an available Spotify Connect device on my computer, tablet, and phone. It's also good for listening to radio station streams. I've got another Echo whose microphone is on. I can ask Alexa on that or in the Alexa app on my phone or tablet to e.g. "listen to KUOW FM on Dot". My Denon A/V receiver predates voice control support (its from 2012 or so), but it does have a network connection with a few control options (TELNET, HTTP). I've got a program running on an RPi that can use the receiver's HTTP interface to get the current input/volume/mute settings, and to change inputs, set volume, and mute/unmute. Apple's "Shortcuts" app on Mac/tablet/phone supports a "run script over SSH" action. I've used that to make a bunch of shortcuts: "Denon Dot", "Denon TV", "Denon Game" to select some sources; "Denon Status" to get the current settings (which the shortcut speaks); "Denon Mute" and "Denon Unmute" to mute/unmute; "Denon Up" and "Denon Down" to slightly adjust the volume; "Denon Set 30", "Denon Set 35", "Denon Set 40", ... to set specific volume levels. Saying the name of a Shortcut to Siri invokes that Shortcut. So putting it all together, A couple voice commands to Siri on any of my Apple devices will switch the receiver to the Dot and set the volume, so it is ready for streaming radio or for Spotify, and if it is radio I want a voice command to Alexa will start that. This has covered pretty much all my "smart" A/V needs, so I can probably happily keep using my existing receiver for quite a while.