The White House said in a statement that Mr. Trump and mr. Xi "agreed North Korea must stop its provocative and escalatory behaviour".
In recent days، Trump and the North Korean regime have engaged in heated rhetoric about the Asian nation's nuclear weapons program.
"These statements are irresponsible and unsafe, and also senselessly provide a boon to domestic North Korean propaganda which has long sought to portray the United States as a threat to their people", read the letter which was spearheaded by Rep. John Conyers of Missouri.
The statement came just hours after Chinese leader Xi Jinping urged Trump in a separate phone call to avoid rhetoric that could inflame tensions with Pyongyang.
"He does something in Guam, it will be an event the likes of which nobody has seen before - what will happen in North Korea", Trump told reporters Thursday from his home in Bedminster, New Jersey.
"You have this guy [Trump] making bellicose threats against somebody else who has very little to lose over there", Ellison said.
It also said that the two "reiterated their mutual commitment to denuclearization of the Korean Peninsula".
Earlier this week Donald Trump vowed that Washington would respond to further threats with "fire and fury", while Pyongyang has accused the U.S. president of "driving" the Korean peninsula to the "brink of a nuclear war".
The Labour leader's intervention comes after China's president warned the U.S. and North Korea not to exacerbate tensions after Mr Trump said Kim would "truly regret" military action.