FBI Director James Comey has cited the dossier in some of his briefings with lawmakers in recent weeks as one of the information sources used by his bureau to bolster its probe, U.S. officials briefed on the investigation told CNN.
The FBI is investigating Russian efforts to interfere in the 2016 election, as well as any potential ties between the Trump campaign and Moscow.
The secret court that oversees the Foreign Intelligence Surveillance Act (FISA) granted the FBI a warrant to monitor the communications of Page, a former national security adviser on Trump's campaign.
The FBI obtained its warrant to monitor Page in the summer of 2016, The Washington Post reported last week.
Page has denied any wrongdoing since news of the warrant last week and has dismissed reports that he provided a Russian operative with classified information.
Officials told CNN that information in the dossier had to be corroborated by the FBI before they could include it in the FISA application, although they would not specify what or how much of the dossier was corroborated.
Top intelligence officials gave President Obama and President-elect Trump a summary of the dossier in December, when its contents first came to light.
The dossier and its claims have been the focus of intense scrutiny.
Comey's mentions of the dossier in briefings to lawmakers contrasts with other U.S. intelligence agencies who have sought to distance themselves from it.
The dossier alleges that Page met top Kremlin officials in an official Trump campaign capacity to discuss U.S.-Russian sanctions, potential business opportunities, and Russia's meddling in the 2016 election.
Page first came on the FBI's radar in 2013 for his communications with a Russian spy. The spy was prosecuted and intelligence officials believe he was trying to turn Page into a source. But Page has denied he knew the person was a spy or that he did anything wrong.
Page visited Russia in July during the campaign, where he criticized U.S. foreign policy toward Russia. Page said his views are his own and do no reflect those of the Trump campaign.
Page has also said the Obama administration is fueling the Russia allegations.
"I look forward to the Privacy Act of 1974 lawsuit that I plan to file in response to the civil rights violations by Obama administration appointees last year," Page told CNN in a statement. "The discovery process will be of great value to the United States, as our nation hears testimony from them under oath, and we receive disclosure of the documents which show what exactly was done in 2016.”
During the campaign, Trump named Page as one of his national security advisers during an interview. Page officially joined the 2016 campaign team from March to September. Page referred to himself a 'junior member of the team,” and Trump aides have also said Page did not play a major role in the campaign.
The dossier is a compilation of memos by a former British intelligence agent, working for Trump political opponents, that describe an effort by the Russian government to find weak points to exploit Trump.
The Washington Post first reported the FISA warrant on Page earlier this month.
FISA warrants are granted sparingly, secretly, and require approval by top Department of Justice and FBI officials as well as a lengthy testimony about why the agency should surveil Page. Proof of crime is not necessary in order to obtain one of these warrants.
CNN reports that other intelligence officials separately concluded Russia interfered in the 2016 presidential election without the use of the dossier.
This story was updated at 7:01 p.m.