Murphy replaced Russian Movsar Evloev for the bout against American Pico after he withdrew from the contest for undisclosed reasons.
Australian Volkanovski said Evloev, who is also undefeated in 19 fights, would have been the number one contender had be beaten Pico, but Murphy has now leapfrogged him.
Volkanovski 36, is a two-time featherweight champion and regarded as one of the best of all time in that class.
He made five title defences before defeat by Ilia Topuria last year, but regained the belt by defeating Diego Lopes in April.
Despite his undefeated record, Murphy’s reserved personality in comparison to some of his brash peers means he has sometimes failed to get due credit for his work in the octagon.
A lack of highlight reel moments, with Murphy earning five straight decision wins before facing Pico, also affected his star power but opinion has started to shift following his spinning elbow knockout.