Judge Phelan is a friend of Detective Jimmy McNulty's who presides over the D'Angelo Barksdale murder trial, watching the jury give a not guilty verdict when a witness changes her statement. After he learns the witness was paid off (and possibly intimidated), and that D'Angelo is part of a much larger drug dealing operation, Phelan insists that Police Deputy Commissioner Ervin Burrell set up a detail to investigate. When Phelan speaks to the press about the murder of another witness from the trial, McNulty feels that Phelan has gone behind his back, souring their relationship for a time.
Over the course of the investigation, he remains willing to sign court documents authorizing wiretaps. When Phelan realizes his actions have cost him political capital, his passion for the case wanes. Assistant States Attorney Rhonda Pearlman uses Phelan's obvious attraction to her to keep him interested in the case.
Phelan reconciles with McNulty in Season three when the judge authorizes a wiretap on Russell "Stringer" Bell's cell phone.