"more significant challenge" is a correct and usable phrase in written English.
You can use it when you are referring to a challenge that is greater in scope or more important than other challenges. For example: "The most significant challenge for the team is developing a reliable and cost-effective solution."
A more significant challenge came from a faction of Greek archaeologists, who viewed the building not as cementing Greece's heritage -- but as cementing over it.
Drilling around or through the salt poses a more significant challenge than drilling through salt layers in the Gulf of Mexico, which are more dispersed, analysts say.
The second, more significant challenge relates to the loss of board awareness of the contributing factors to Sarbanes-Oxley: the governance failures of the Enron board.
But a big jump — combined with tensions over Iran and continuing European debt worries — could present a more significant challenge to America's recovery, they say.
However, a number of scientists said that mapping and understanding the human brain presented a drastically more significant challenge than mapping the genome.
The cause of anti-Libya alliance should not diminish the more significant challenge of pressing the Arab states toward adjustment of their national compacts.
There are more significant challenges.
Then again, Mondonico has overcome more significant challenges in the past 13 months.
This scenario poses more significant challenges than only avoiding dropping the voice call.
The management of collected tephra was viewed by farmers as one of the more significant challenges during the eruption.
Although widespread use is made of this assumption, its justification is one of the more significant challenges for the foundations of statistical mechanics.
