Hi

 Sonos will pick up music stored on your phone if you choose the source to be 'on this mobile device '

If you choose Music Library it will play music stored on your.PC (assuming that it where your Miusic Library is pointed).

Tbh I am a bit puzzled by your post. This is already totally in your control. 

So I let others access my phone controller to select music, (stored on laptop) but also have my personal selections stored on my phone micro sd which I want kept private.

Perhaps I should ask if its possible to remove "on this mobile device" option? 

No, that’s a permanent option in the software. You don’t have to select it, though. It just can’t be made to disappear. 

Get an old-ish iPhone and give that to the “others”, it won’t have the “on this mobile device” feature. Or for that matter get another Android device which obviously wont be able to access your files on your phone.

So you lend them the phone to play music on your system and you're not there to 'police' what they do?

Yep. 

But the question I asked is still the same...…

Can I stop sonos seeing music stored on my mobile phone.? 

@freddy 224, Only those to whom you hand over your phone, are able to see and play your music files stored on your phone. Switch off your phone, and neither you will have access to these tracks.

OK. In that case the answer is still the same. No.

Of course they could download the app onto their own phones. That would mean giving them your WiFi password  of course. But if you trust them with your phone...

Actually, maybe yes. In the app Settings on your phone remove the storage permission from the Sonos app.

Edit. In fact that isn't so good. It is easy for anyone on your phone to grant permission again. But if you already trust them not to completely screw your phone up when you hand it over …