The West was lucky enough to invent penicillin which rather limited the appeal of phage research- you don't need phages if you haven't discovered antibiotic resistance, and once you've committed to using broad-spectrum antibiotics you'll just do what we did, which is switch between them.

It sounds like the USSR was just not very good at producing its own antibiotics, so phage therapy remained popular there, as it wasn't any less effective than their poor quality antibiotics, which ended up causing resistance there before they did in the West. If you've managed to spur resistance, and you have persistent supply problems with your antibiotics, pushing forward with phage research makes a lot of sense.

http://discovermagazine.com/2017/oct/the-cold-wars--modern-r...