Key Inclusion Criteria:  Cystic fibrosis patients with chronic Pseudomonas aeruginosa pulmonary infection receiving standard of care CF medications Age ≥ 18 years FEV1 ≥ 40% predicted Clinically stable lung disease Willing and able to provide adequate sputum samples, using any method (spontaneously expectorated, induced, from home or clinic) at designated study visits.  Key Exclusion Criteria:  Known hypersensitivity to bacteriophages or excipients in the formulation. Receipt of prior bacteriophage therapy within the 6 months prior to Screening Recovery of Burkholderia species from respiratory tract within 2 years prior to screening Currently receiving treatment for allergic bronchopulmonary aspergillosis Currently receiving treatment for active infection with non-tuberculous mycobacteria History of severe neutropenia History of lung transplant History of solid organ transplant Acquired or primary immunodeficiency syndrome Initiation or change in CF modulator therapy less than 3 months prior to screening Pregnant or breastfeeding female