Multi-drug-resistant Pseudomonas aeruginosa (P. aeruginosa) commonly causes infections that are difficult to treat, necessitating the development of new therapeutics. The search for more effective ways to combat the emergence of bacterial resistance has also led to research into phage-antibiotic synergy (PAS) as a potential therapeutic strategy. The aim of this study was to isolate and characterize virulent phages from water sources that are active against clinical carbapenem-resistant P. aeruginosa isolates, and to evaluate their in vivo efficacy using a Galleria mellonella larvae infection model. The biological and genomic characteristics of the isolated phages were determined using host range analysis, one-step growth curve analysis, transmission electron microscopy analysis and whole-genome sequencing. Two phages (vB_PaMB13 and vB_PaMB17) that demonstrated in vitro synergistic and bactericidal interactions with antipseudomonal antibiotics (tobramycin and ceftazidime) were selected for further investigation using the checkerboard method. The study revealed synergy between all phages and either antibiotic, tobramycin or ceftazidime, against P. aeruginosa. Similarly, the percentage survival rates increased in the in vivo model when both phages and antibiotics were used in combination. Overall, our study provides further support for the idea that phage-antibiotic synergy could be an effective strategy for improving treatment outcomes.