Really fascinating area of science. They were ignored in lieu of antibiotics in the post war forming of big Pharma (except for pockets like France and Russia). Startups are working in this space now https://www.phagos.org/
And that's if you're lucky. Some bacteria replicate under extremely obnoxious conditions, and sometimes the phages will only generate double-digit levels of virion particles each generation as opposed to the triple-digit target you want, and all your attempts to optimize the system hit a brick wall. Ask me how I know? :)
But if the library fails, and you need to find and mass-produce a new phage, the pipeline starts over again. That is what I was referring to in my previous comment. I have worked with certain gut bacteria that can be infected by phages, but those phages replicate in the tenfold range rather than the hundredfold range you see with bacteriophages like for E. coli. Growing such bacteria at bioreactor scale is challenging enough before you add in a phage that, by its nature, does not replicate at the scale you need. And post-reaction, filtering out the phage into something safe like saline can lead to more loss of phage, which I have also seen happen.