Wayne Bennett's Three Lions have booked their quarter-final spot after they eased past France at the weekend and Roby was the star of the show with Bennett singling out the St Helens star for praise.
Roby is battling it out with England's regular hooker Josh Hodgson for the starting spot against PNG and says he will find out during the week who will get the nod to start.
"Wayne will speak to us during the week and tell us what his team selection is," said Roby. "There's good rivalry in this squad in pretty much every position. They're all quality players.
"Obviously myself and Josh are rotating in training but that's the same for the other players. We're all competitive by nature and it probably brings out the best in us without us even realising it sometimes."