Yes, when you group the Port/Turntable setup with your Arc/Sub setup, the music from your turntable will play through the Arc and Sub.

Actually you don’t need to necessarily ‘group’ the two Sonos devices, as suggested, although that’s one way to use them, you can just select the Port ‘line-in’ as an audio source and play the TT audio direct to the Arc without it playing to the Port too. So there’s plenty of choice with these two Sonos devices.

Note that a turntable needs to either have a built in preamp, or an external preamp between it and any Sonos device.

thanks all - but how / where in the app do I tell Port to send audio to the Arc and Sub I have setup on the TV?

nevermind, got it sorted and the TT was not set to Line - thanks all!

This briefly outlines a manual method:

With the TT playing via the Sonos Port ‘line-in - In the Sonos App, select your Arc as the playing room from the system/rooms tab (middle icon on main toolbar) and then goto the Browse Tab (music icon on main toolbar) and select the ‘line-in’ icon as your chosen audio source  (the icon is at the end of the list of available music services/sources) … and it will then play the TT audio to the Arc. 

There is an option to ‘Autoplay’ the line-in audio source too, via the Ports room settings in the App in "Settings/System/ Port Room Name]” the various Autoplay options are fairly self-explanatory.