The first-choice pairing have helped prevent defeat for England in the last 10 games that they have started together.
"I remember playing with Phil the first time and people were talking about the fact that Rio has gone and JT has gone, but over time [our partnership] has got stronger and stronger and better," BT Sport quotes Cahill as saying.
"We have got a better understanding, a better partnership together when we have played in these games. More importantly we have not conceded too many goals so that is pleasing and I hope that continues if we are paired together [in Brazil]."
England will play three warm-up friendlies before their World Cup campaign gets underway against Italy on June 14.