Why don't they try phage therapy instead of a vaccine for the covid virus? there's some promise that it helps with antibiotic resistant infections, maybe good bacteria can attack it?

Phage therapy: Phage treatment has never proved useful for curing or treating a viral infection in humans. It's a nice theory, and my guess is that coronavirus researchers are looking into it. Of course no treatment ever should be "instead of a vaccine": both treatments and vaccines are necessary.

Bacteria: Bacteriophages can destroy bacteria but not viruses. No phages capable of destroying SARS-CoV-2 is known. Have a healthy diet, exercise 30 minutes/day, drink plenty of water, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV vaccine. Wish you good health!