On the eve of a planned vote by a Senate committee on whether to hold Dr. Anthony S. Fauci in contempt of Congress for refusing to answer questions at a hearing last week, the chairman of a separate panel said that he has obtained a copy of Dr. Fauci’s cellphone.

“Hopefully, this device will address many of the questions he refused to answer at last week’s hearing,” Senator Ron Johnson, Republican of Wisconsin and chairman of the Senate Permanent Subcommittee on Investigations, wrote on social media Wednesday night.

Like Senator Rand Paul, the Kentucky Republican who ordered the contempt vote, Mr. Johnson has been a fervent critic of Dr. Fauci. While Mr. Paul has focused his inquiry on the origins of the pandemic, Mr. Johnson has been more interested in Covid vaccines.

News that Mr. Johnson had obtained the phone was first reported by The Wall Street Journal, which said that the Department of Health and Human Services had sent a copy of the phone to Mr. Johnson’s subcommittee.

A spokesman for Dr. Fauci did not return a text message seeking comment late Wednesday.

During last week’s hearing before the Homeland Security Committee, Dr. Fauci invoked his Fifth Amendment right to remain silent more than 100 times, following a brief opening statement in which he said that Mr. Paul, the panel’s chairman, had an “unhinged obsession” with him.

The senator, who has repeatedly said he wants to see Dr. Fauci in prison, has accused Dr. Fauci of funding research in China that created the virus responsible for the Covid pandemic, and lying to Congress about it. Dr. Fauci, who appeared before the committee under a subpoena, has vigorously denied the allegation.

Senator Paul and his fellow Republicans assert that, because Dr. Fauci received a “pre-emptive” presidential pardon from former President Joseph R. Biden Jr., he does not have the right to invoke the Fifth Amendment.

They also say that Dr. Fauci’s brief statement at the outset of the hearing amounted to testifying, and that he cannot both testify and refuse to testify.

“Accountability is coming,” Mr. Paul wrote on social media Wednesday, above a photograph of Dr. Fauci at the witness table that said, “Dr. Fauci’s Contempt Vote. Thursday at 8:30 a.m.”

If the Homeland Security Committee votes to hold Dr. Fauci in contempt, it would clear the way for the panel to recommend that the Justice Department prosecute him for failing to comply with the subpoena, a misdemeanor under federal law. But that does not mean the department will take up the case.

In order for a contempt resolution to carry the force of law, the full Senate must adopt it. If that happens, it would be sent to the U.S. attorney in Washington, who would then have an obligation to investigate. But contempt resolutions require a 60-vote majority, and with 53 Republicans in the Senate, adoption is highly unlikely.

Mr. Johnson’s announcement comes less than two weeks after Senator Paul publicly released Dr. Fauci’s journal, which Health Secretary Robert F. Kennedy Jr. turned over to the committee.

The journal, written on a government computer, exposed Dr. Fauci’s interest in his own media appearances and friendships with celebrities, a stark contrast to the white-coated scientist many Americans had come to know. It also revealed that Dr. Fauci had academic colleagues to nominate him for cash prizes, including a $1 million award from an Israel-based foundation, which government ethics officials allowed him to keep.

Republicans have used those diary entries to accuse Dr. Fauci of using his government position to enrich himself. But the diaries also show that Dr. Fauci sought the required ethics approvals, and that officials instructed him to turn down some awards.

Whether or not the resolution is adopted, the Senate vote will not mark the end of Dr. Fauci’s travails. The attorney general of Florida, James Uthmeier, announced Wednesday that he has issued a subpoena for Dr. Fauci and is teaming up with the attorneys general of West Virginia and Louisiana to investigate the scientist for “potential self-dealing during the pandemic” and Covid-19 guidance that affected Florida businesses and consumers.