Answered Dec 26, 2018
As the name suggests, bacteriophages infect bacteria. They cannot infect humans, other animals, or plants.
However, some phages have genes that code for peptide toxins, which are then released by the bacterium host.
So the phage infects the bacteria, and provides the genetic information to produce the toxin. When you get infected by the bacteria (e.g. from contaminated water or food), it releases the toxin, which makes you sick.
This is kind of a symbiotic relationship between the phage and the bacteria species. The phage gets to spread and reproduce itself, and the bacteria receives information to become more virulent. When the toxin induces diarrhea, that helps to spread the bacteria host and the phage inside it.
Human diseases involving phage coded toxins include botulism, cholera, diphtheria, scarlet fever, and a few others. Here is a list.