The Democratic establishment and major donors have already lined up behind Mr. Biden, who raised $71.3 million with the Democratic National Committee and his joint fund-raising committee during the three-month reporting period that ended Sept. 30.
Mr. Phillips will also need to work fast to get his name on the ballot in several early-voting states. Already, he has missed the deadline to appear on the ballot in Nevada, the second nominating state on a new presidential primary calendar approved by the national committee this year.
Mr. Phillips, 54, has for months stressed his belief that Mr. Biden, 80, should face a serious primary challenge, citing the president’s age and low approval ratings as evidence that Democrats are eager for a new generation of candidates. (Several Republican candidates have made similar arguments in their bids against former President Donald J. Trump, who is 77.)
An heir to a Minnesota liquor company who also ran the gelato company Talenti, Mr. Phillips was first elected in 2018, as part of a wave of Democrats who flipped Republican-held suburban districts in a backlash to Mr. Trump. He stepped down from a position in Democratic leadership in the House this month as he weighed joining the presidential race.
Mr. Phillips will join two other primary challengers to the president: Marianne Williamson, the self-help author who unsuccessfully ran against Mr. Biden in 2020, and Cenk Uygur, the co-creator and co-host of the progressive talk show “The Young Turks.”