Phages are the most ubiquitous organism on Earth. They are naturally occurring viruses that infect bacteria and bacteria only. We live in a sea of phages. Our bodies are more phage than human. There approximately 10 to the 32 power of them around us. That's 10 with 32 zeros behind it.
Antibiotics cannot keep up with evolving infections, while phages naturally co-evolve with the bacteria.