Lehigh Valley began December with a four-game losing streak, starting with a 3–1 loss to Springfield on December 4 despite a franchise-record 63 shots by Lehigh Valley. Greg Carey also set a single-game franchise record with 14 shots on goal, and opposing goalie Philippe Desrosiers' 62 saves was the most ever made against the Phantoms by an opposing goalie. All three of those previous records had been set in a Philadelphia Phantoms game against the Cincinnati Mighty Ducks on January 6, 1999, when the Phantoms made 60 shots, Richard Park made 13 shots on goal, and Tom Askey made 61 saves against Philadelphia. Bunnaman scored a goal in the December 4 game that made him the 23rd Phantom to score in 2019, the most in the AHL to that point. December 6 marked the 200th professional game for Andy Welinski and Reece Willcox; all of Willcox's games were with Phantoms. Kyle Criscuolo reached his 200th game on December 7, which also marked the 227th game for Nicolas Aubé-Kubel, the fifth most of any player in Lehigh Valley history. The Phantoms 1–0 loss to the Hershey Bears on December 7 was the fifth straight game between the two teams to be decided by one goal, the first 1–0 loss for the Phantoms since they came to Lehigh Valley in 2014, and the first 1–0 loss in 249 games against Hershey dating back to 1996. As of that game, the Phantoms had a league-leading 18 games decided by one goal, out of 25 season games played in total. The Phantoms also lost 4–0 to Hartford on December 13, their second straight shutout loss, and the third one of the season. December 13 saw the return of Andreoff, Rubtsov, Maksim Sushko, Chris Bigras, all of whom had been out three weeks or longer due to injury. A December 21 game against Charlotte saw the AHL debut of left-wing Max Willman, and Bigras' first multi-point game with Lehigh Valley, both assists. Laberge also scored two goals, his third multi-goal game in 28 contests. Charlotte beat the Phantoms 4–2 the next day, the first time in six games on the season that the defending Calder Cup champions defeated Lehigh Valley in regulation. It also marked the first of a four-game losing streak for the Phantoms. Carey scored his team-leading ninth goal of the season on December 22.