Phages are pretty cool, but bacteria do develop phage resistance as well. Phages also can evolve to evade those resistances, in a co-evolutionary battle, but also Phages can still be seen as antigens to our own body.

A recent case-study: https://www.upmc.com/media/news/021424-phage-therapy

To avoid reading the whole article: Antibiotics no-longer worked for a patient in 2020 that developed an infection after needing immunosuppression for treatment of an autoimmune condition, so they tried phage therapy.

quote from the phage treatment section:

Within 24 hours of receiving phage therapy, the patient’s blood infection had resolved and she could go home, where she continued the phage and antibiotic combination. She developed a few short-lived breakthrough infections, which indicated the bacteria was getting around the therapy, so the researchers found an additional phage that targeted her bacteria.

With the addition of the new phage, the patient was blood infection-free for four months and able to travel out of state for a for a family beach vacation.

However, just over six months after starting phage therapy, the blood infection returned, and the phage-antibiotic combination was thought to be no longer effective. The patient died in 2022.

In order to learn why the infections recurred despite the combination being previously effective, laboratory testing revealed that the patient’s immune system had likely activated in a way that blocked the phages from attacking the bacteria.

I'm not disagreeing with the benefits of Phage Therapy, just that it isn't likely a magic solution all on it's own, and can still suffer similar resistance issues as antibiotics have. I'm a fan of multipronged attack vectors, to reduce the chance of developing progressive resistances (ie. wipe out the whole colony), and the more tools we have for that, the better.