Manuel had been working as an adviser in the team's front office. The move is not expected to be long term, a source told Todd Zolecki of MLB.com.
General manager Matt Klentak said the club isn't considering any further coaching changes at this time, and that Manuel will join the team Wednesday.
The 75-year-old spent nine years as the Phillies' skipper from 2005-2013, which included a World Series victory in 2008. Manuel built a reputation as a hitting coach with the Cleveland Indians before that, with Hall of Fame slugger Jim Thome crediting him for his success, according to Zolecki.
Philadelphia was expected to be one of the league's best-hitting teams this season after adding several stars through free agency and trades during the offseason. However, the offense enters Tuesday's action ranked 24th in the majors in batting average (.245), 23rd in slugging (.417), 18th in on-base percentage (.322), and 16th in WAR (14.5).
Outfielder Bryce Harper's .844 OPS is down from his career .893 mark, All-Star catcher J.T. Realmuto sits at .774 after posting an .825 season in 2018, third baseman Maikel Franco (.702) was demoted to the minors, and outfielder Andrew McCutchen saw his campaign end in June after tearing an ACL.
The Phillies (60-58) sit nine games back of first place in the NL East and two games out of the second wild-card spot.