It depends.  What kind of earphones?  Does the turntable have a headphone jack?

Not sure if the Sonos turntable does I’ll check. Can use jack or Bluetooth 

Just come off their helpline and you’d have to buy the Sonos port which is around £399

Not if the turntable has a headphone jack.  If it does, just plug the headphones into that. 

And if the TT doesn’t have a headphone jack simply use an RCA splitter to feed the Era and a headphone amp (or transmitter) at the same time. 

I can’t think why the helpful rep suggested a Port, unless that was to feed anything playing on the Sonos system to headphones. In any case you’d still need a headphone amp (or transmitter).