Phage must carry out specific set of reactions in order to make more of themselves.
First, the phage must be able to recognise a bacterium that can multiply in by binding to the bacterial cell surface.
Next, the phage must inject it’s genome and the genome must be protected from the bacterial nucleases in the cytoplasm.
The phage genome must be replicated transcribed and translated so that a large number of genomes, capsid proteins, and tail proteins, if present, are produced at the same time. Complete phage particles are then assembled and the phage must get back out of bacterium.