RecruitingBehavioural interventionACT With CF Self-Help ToolkitAcceptance and Commitment Therapy (ACT) tailored to meet the needs of adults living with cystic fibrosis (ACT with CF) is a newer form of talk therapy that has been shown to reduce anxiety \& depression and improve psychological flexibility, and value-based living. The investigators are now trying to find out whether a self-help version of this treatment (ACT with CF - Self Help Toolkit) is also effective in reducing anxiety and depression and improving psychological flexibility and value-based living in adults with CF. Adults with cystic fibrosis are at increased risk for anxiety and depression. This study examines whether a patient-facing therapy, ACT with CF - Self Help Toolkit can help to reduce anxiety and depression among adults with CF. This treatment can be accessed on the participant's smartphone.