Phillips missed the 2-0 win at home to Huddersfield Town in March with a knee injury but comes back into the side for Gaetano Berardi who drops to the bench as Ben White moves back to centre-back.
Roberts, meanwhile, replaces Pablo Hernandez who has suffered a setback but Leeds are hopeful the Spaniard will be back available for next weekend's hosting of Fulham.
Jean-Kevin Augustin also needs necessary individual fitness work and is missing while Adam Forshaw remains sidelined as he continues to recover from hip surgery and Kiko Casilla remains suspended.
A nine-man Leeds bench also features January recruit from Manchester City Ian Poveda but Barry Douglas misses out with a calf injury.
Like Hernandez, Douglas is also expected to be in training next week in contention for Fulham.
Forward Lee Tomlin only makes the bench for Cardiff along with winger Nathaniel Mendez-Laing.
Forward Tomlin's 2019-20 campaign was thought to be over after the 31-year-old injured his knee in training in February on the back of an impressive start under Harris that featured seven goals and seven assists in the current term.
Winger Mendez-Laing, meanwhile, was also ruled out for the remainder of the season after rupturing his hamstring in the clash against Sheffield Wednesday at the end of December.
But both have to make to do with places on the bench whilst Jazz Richards (calf) and Greg Cunningham (ACL) are also missing.
Cardiff City: Smithies; Sanderson, Nelson, Morrison, Bennett; Adomah, Vaulks, Bacuna, Ralls, Hoilett; Paterson. Subs: Etheridge, Flint, Smith, Pack, Whyte, Tomlin, Mendez-Laing, Ward, Glatzel.
Leeds United: Meslier, Ayling, White, Cooper, Dallas, Phillips, Klich, Harrison, Costa, Roberts, Bamford. Subs: Miazek, Berardi, Alioski, Struijk, Davis, Gotts, Poveda, Shackleton, Stevens.