Clostridium difficile infection (CDI) is a global health problem causing infectious diarrhoea, ulcerative colitis and death in ~10% cases. The conventional antibiotic CDI therapy can result in treatment failure and recurrent infection. C. difficile produces biofilms, which impair antibiotic activity. Phages could potentially penetrate these biofilms and be developed to either replace or enhance antibiotics. We determined the efficacy of prophylactic and remedial regimens of an optimised 4-phage cocktail in both biofilm and insect models. This was done as a stand-alone treatment, and, as adjunct to vancomycin. Biofilms of six clinical strains were established and subjected to phages/vancomycin and the impact on the biofilms was analysed according to viability counts, turbidity and topography as observed using scanning electron and confocal microscopy. The phage/vancomycin regimens were also tested on an optimised Galleria mellonella larvae CDI model. The infectivity profiles and efficacies of orally administered phages and/or vancomycin were ascertained in vivo by monitoring colonisation, survival rates and differential expressions of 28 G. mellonella stress markers. The different strains produced distinct proportions of spores and vegetative cells in the biofilms. Whilst both phages and vancomycin impacted on biofilm properties, phages compared favourably to vancomycin, prevented biofilm formation and penetrated established biofilms. Phage application resulted in reduced colonisation in the larvae model, with extended longevity in remedial treatment but complete recovery in the prophylaxis regimen. The activity is comparable to vancomycin and the combined treatments. Furthermore, an analysis of the insect infection and growth markers revealed that phages clearly reduced infection and enhanced insect growth. Taken together, our data suggest that phages have a significant prophylactic effect on biofilms, and prevent colonisation of C. difficile in the larval model. The ability of the phages to penetrate biofilms could enhance the efficacy of commonly used antibiotics against CDI.