The Phantoms are on the brink of elimination after a 5-0 loss Wednesday to visiting Toronto in the AHL's Eastern Conference finals.
Ben Smith scored two goals and Garret Sparks made 16 saves and notched the shutout. The Marlies lead the series, three games to none, and can advance to the Calder Cup finals if they beat the Phantoms on Friday in Allentown.
Lehigh Valley had just nine shots over the first two periods and fell into a 3-0 hole.
Trailing 1-0, the Phantoms applied lots of offensive pressure, but the Marlies scored a back-breaking goal when Andreas Johnsson's pass went off the skate of Lehigh Valley's Cole Bardreau and past goalie Alex Lyon.
In the third period, a frustrated Lyon kicked Mason Marchment when he was in the crease, getting a five-minute major and a game misconduct.