A report on Major League Baseball's official website said the Marlins would get catcher Jorge Alfaro, right-hander Sixto Sanchez and leftie Will Stewart in the deal.
The Marlins would also receive $250,000 in international bonus slot money as part of the deal, which was complete pending physicals.
Realmuto is regarded as one of the best catchers in Major League Baseball and made the All-Star team in 2018 for the first time.
The 27-year-old from Oklahoma batted .277 last season and tallied 21 home runs and 74 RBIs during the season, both career highs.
The Phillies sweetened the deal by offering Sanchez into the bargain. The 20-year-old Dominican is one of the Phillies' best pitching prospects.
Realmuto joins a Phillies team which is showing signs of improvement despite not reaching the playoffs since 2011.
The 2008 World Series champions finished 2018 with a 80-82 record after a 66-96 campaign in 2017 and a 71-91 record a year earlier.