After compiling a record of 17–9 (1), Phil Harris signed with BAMMA in 2010, making his debut against Irish featherweight Steve McCombe at BAMMA 2, winning via unanimous decision. He followed that up with another decision victory over Neil Seery at BAMMA 3. After a 21-month layoff, Harris dropped two weight classes to take on Canadian grappler Remi Morvan at Cage Warriors 46, winning by triangle armbar at 4:21 of round 1, his first submission win since 2007. Less than a month later, he took on TUF 14 contestant Casey Dyer at Cage Warriors: Fight Night 4, notching his fifth consecutive win with a unanimous decision.
On August 16, 2012, Harris was signed by the Ultimate Fighting Championship. He made his UFC debut against fellow grappler Darren Uyenoyama at UFC on FX 5 on October 5, 2012, replacing an injured Louis Gaudinot. Harris was submitted in the second round with a rear naked choke.
Harris next faced Ulysses Gomez on February 16, 2013 at UFC on Fuel TV: Barao vs. McDonald. Harris won the bout via unanimous decision.
Harris was expected to face John Lineker on August 3, 2013 at UFC 163, but Harris suffered a fractured orbital bone in training and he was replaced by José Maria.
The bout with Lineker was rescheduled for October 26, 2013 at UFC Fight Night 30.