Phillips joined the crew of Showtime television drama Dexter as a writer and executive producer midway through the first season in 2006. He was nominated for the Edgar award for Best Television Episode (Teleplay), for writing the episode "Crocodile".
He returned as an executive producer and writer for the second season. Phillips and the writing staff were nominated for a Writers Guild of America Award for best dramatic series at the February 2008 ceremony for their work on the second season. Phillips remained an executive producer and writer for the third season. The writing staff were nominated for the same award at the February 2009 ceremony for their work on the third season. Phillips remained an executive producer and writer for the fourth season but in addition became the series show runner. Phillips and the writing staff was nominated for the WGA award a third consecutive time at the February 2010 ceremony for their work on the fourth season. Phillips stood down as show runner after the fourth season and left his role as an executive producer. He was credited as a consultant on the fifth season.
Phillips joined Nurse Jackie for season five, where he now serves as showrunner and executive producer.