The Sonos Amp doesn’t have a Bluetooth system associated with it, you’d need to send the Bluetooth signal into the Sonos ecosystem using a device that does, and then ‘group’ that device with your Amp. 

Hi Bruce

Thanks for your reply. Apologies, I didn't state my question very clearly. I realise that the amp does not have Bluetooth functionality, and I mentioned  Bluetooth just as an analogy. To phrase my question a little better: given that my phone and the Sonos Amp are connected to the same wifi network, can I use that network to send audio from my phone to the amp?

I'm guessing the answer is no, or I probably would have found the way to do it by now.

While not operationally convenient, you could use a Bluetooth to RCA Jack receiver accessory connected to AMP.

Androids don’t have AirPlay 2 capability, and Google has chosen not to make ‘casting’ available on Sonos, so there isn’t an ‘easy’ way, without doing something like ​@buzz suggests, or copying the music onto a computer HD or NAS and setting up a local library. 

Thanks for the feedback. I'll get a Bluetooth RCA adaptor. Logitech have a well reviewed one.

Hi ​@peter12381 

Welcome to the Sonos Community!

You’ve been excellent advice above, but if it is a Samsung device that you happen to have, then you can use SmartThings to play to Sonos - just open the Samsung Music app and tap the icon in the top corner to use SmartThings to send the music playing in Samsung Music to your speakers.

I hope this helps.