Castellanos had three hits and scored three times. Bryson Stott also had three hits and Brandon Marsh drove in three runs for the Phillies, who claimed their first NL East title in 13 years on Monday night.
READ MORE: Phillies clinch 1st-round bye; NLDS will start in Philadelphia as race remains tight for No. 1 seed
Coupled with Milwaukee's 2-1 loss to Pittsburgh, Philadelphia secured the bye and home-field advantage in the NLDS. The Phillies owned the tiebreaker with the Brewers after winning the season series against the NL Central champions.
Nico Hoerner homered twice for Chicago, and Isaac Paredes hit four singles. The Cubs lost two of three in the series to finish with a 39-42 road record.
Philadelphia closed out the home portion of its regular season with a 54-27 mark. A crowd of 42,438 was on hand for the 47th sellout of the season, running the home attendance to 3,308,638 on the year.
The Phillies finish with three games at Washington, beginning on Friday. Philadelphia can clinch home-field advantage through the NL Championship Series by ending the season tied with or ahead of the Los Angeles Dodgers, who entered Wednesday a half-game in front of the Phillies at 93-64.
Turner put Philadelphia in front with a one-out solo shot in the first. Stott added a two-run double against Javier Assad (7-6), lifting the Phillies to an early 3-0 lead.
Castellanos added another solo shot in the third, but Hoerner responded with a three-run shot off Cristopher Sánchez in the fourth.
Marsh gave Philadelphia an 8-4 lead with a three-run double off Keegan Thompson in the fifth. All three runs were charged to Assad, who was charged with eight hits in 4 1/3 innings.
Sánchez was charged with four runs, three earned, and five hits in 4 2/3 innings. José Ruiz (5-1) got four outs for the win.
Kevin Alcántara, one of Chicago's top prospects, started in right field and singled in the ninth for his first major league hit.
TRAINER'S ROOM
Cubs: 1B Michael Busch (right triceps contusion) was not in the lineup, one night after being hit by a pitch in the second. ... OF Seiya Suzuki (ankle) also was sidelined after getting injured running the bases on Tuesday night.
Phillies: Austin Hays started in left field for the second straight day after returning Monday from a stint on the injured list since Sept. 1 due to a kidney infection. He went 0 for 4 with a strikeout.
UP NEXT
Cubs: Following an off day, RHP Jameson Taillon (11-8, 3.41 ERA) starts on Friday against Cincinnati in the opener of a three-game home series.
Phillies: LHP Ranger Suárez (12-7, 3.15 ERA) starts on Friday against the Nationals.
The Associated Press contributed to this report.