So, the way I see it there would be a large wall type thing that symbolizes the front side of "The Pheonix," that way you can still see people on the otherside. Dromio of Syracuse would be sitting in aq chair on one side of the wall when Antipholus of Ephesus (AE) enters from stage left with Dromio of Ephesus (DE) and the two others. Then when the argument starts, it's obvious that neither party can see the the other but then the audience gets to see both of them. This particular scene would be considered more presentational than representational because it would add to the hilarity of the quarrel. AE and DE would be absolutely furious, probably pacing and shaking their fists at the "Pheonix Wall" while shouting at the top of their lungs, whereas Dromio of Syracuse (DS) would be incredibly laid back and making a mockery of AE in front of his guests. I think DS would be more presentational when it comes to interacting with the audience than AE or DE because it wouldn't fit with their characters' mindset at that time.