This study isolated and characterized a novel lytic bacteriophage (vB_LmoS-PLM9) and evaluated its antibacterial efficacy alone and in combination with cinnamon bark and cinnamon cassia essential oils against Listeria monocytogenes in broth, milk, and smoked salmon. The phage remained stable over a broad range of temperatures (4–50°C) and pH values, and genome analysis confirmed the absence of virulence and antibiotic resistance genes. The combined treatment exhibited a synergistic antimicrobial effect, significantly reducing bacterial populations and suppressing the regrowth of phage-resistant cells, particularly in milk stored at 4°C, where bacterial counts decreased below the detection limit. These findings demonstrate that combining bacteriophages with cinnamon essential oils is a promising natural strategy for controlling L. monocytogenes and improving food safety.