Theofilos Xenidis, better known as Phil X (born 10 March 1966), is a Canadian  guitarist and co-founder of the Los Angeles-based turbo pop band Powder. He also has a second band, parody-rock band the Drills. He is best known as the guitarist who replaced Rik Emmett in the Canadian rock band Triumph, for the Edge of Excess album and tour.
An early opportunity in Xenidis's career came when he was asked in 1990 to tour with Randy Coven, whom he met through Aldo Nova; in 1991, he toured the US with Aldo Nova.
Phil X is a prolific session guitarist, having played on albums by Tommy Lee, Methods of Mayhem, Avril Lavigne, Kelly Clarkson,Orianthi, Rob Zombie, Chris Daughtry, Alice Cooper, Thousand Foot Krutch and many others. He wrote the song "Tired" and also played guitar on Tommy Lee's Tommyland: The Ride album. He has appeared with Lee on Ellen and The Tonight Show with Jay Leno. Phil X was featured in the "making of" video for the movie Josie and the Pussycats. He, along with his Powder bandmates, taught the young actresses to appear as if they were actually playing their instruments.
He has performed with the band Frozen Ghost. Phil X is also the inventor of the "Flip Stick," an innovative replacement for the "whammy bar" on Floyd-Rose-equipped guitars.
Since 2008, Phil X has been a faculty member of Camp Rock, a camp in Ontario for aspiring musicians.
In April and May 2011, Phil X substituted for Bon Jovi's lead guitarist Richie Sambora, who could not be present for the required dates. He played the last 13 American shows of Bon Jovi's 2011 world tour.