(written from a Production point of view)
Phelan made his feature film debut in 1987's The Hidden, which featured Michael Nouri, Ed O'Ross, William Boyett, and Larry Cedar. In 1993, Phelan had a supporting role in the independent science fiction film Monolith, along with Boris Lee Krutonog and Musetta Vander. Phelan again co-starred with Vander in the 1995 film Project Shadowchaser II and in the 1999 film Molly.
Before appearing in Star Trek, Phelan appeared in films with two other actors from that film. He was in Servants of Twilight, a 1991 horror thriller which starred Bruce Greenwood, after which Phelan had a role in the 1993 thriller Live Wire, which starred Ben Cross. Patrick Massett and Carel Struycken also co-starred in the former; Tony Plana had a supporting role in the latter. Phelan also starred with George Segal, Elliot Gould, Paige Turco in "The November Conspiracy".
Phelan's other film credits include Stand and Deliver (starring Rosana DeSoto), Cold Feet (starring Keith Carradine and Vincent Schiavelli), Another 48 Hrs. (with Bernie Casey, David Anthony Marshall, Ed O'Ross, Kevin Tighe, and Biff Yeager), Ricochet (with John Cothran, Jr., Tim de Zarn, Sherman Howard, Carlos Lacamara, and Albie Selznick), Doctor Mordrid (starring Jeffrey Combs and Brian Thompson), Boiling Point (with Seymour Cassel), and Overdrive (with Bill Bolender).
On television, Phelan has made co-starring appearances on such programs as Scarecrow and Mrs. King (with Lawrence Dobkin), Tour of Duty (with Patrick Kilpatrick), Knots Landing (starring Michelle Phillips), Gabriel's Fire (starring Madge Sinclair), Life Goes On (starring Bill Smitrovich), Picket Fences (with Michael Keenan), L.A. Law (with Corbin Bernsen, Lawrence Dobkin, Larry Drake, Natalia Nogulich, and Randy Oglesby) and two episodes of Murder, She Wrote, including one with George Takei in 1987. Some of his notable made-for-TV movie credits include Police Story: Burnout with Patrick Massett, From the Files of Joseph Wambaugh: A Jury of One with Dan Butler, Glenn Morshower, and Margot Rose, and A Case for Murder with Robert DoQui, Samantha Eggar, Rosemary Forsyth, Bruce French, Thomas Kopache, Eugene Roche, and Stephen Rowe.
More recently, Phelan has been seen on such television series as The Fresh Prince of Bel-Air (starring James Avery), Weird Science (with Daniel Riordan), and Buffy the Vampire Slayer (with Armin Shimerman). In 2001, he had a recurring role as Mac on NBC's daytime drama series Passions.