In general, an analog line in (should be line level, not phono level) is changed from analog to digital by the line in, and then forwarded to the rest of Sonos as necessary. If it’s sent back out to the line out, that is after conversion to digital, and then back to analog and not a straight pass through.

Thanks Bruce that’s what I was looking for.  Just for clarity, I have the turntable connected to a phone state preamp before the Sonos line in.  Works fine, I just did not know if I was going through two conversions or not.

Yes. One going in, another going out. There is no ‘pass through’ option available on a Sonos device.