The goal of this clinical trial is to help adolescents and young adults between the ages of 13-25 with Cystic Fibrosis (CF), medically stable, able to speak and read English, and are not experiencing a CF - related exacerbation, who are already active to remain, or gradually encourage them to increase their levels of physical activity

Participants will be asked to utilize a smartphone program, called NUDGE that we have developed. NUDGE is a chatbot with evidence-based features known to help teens make progress toward health goal:

• Set and review goals
• Self-monitor progress
• Provide feedback on goal attainment
• Revise future goals

The goal of this study is to conduct a 6-month delayed treatment pilot Trial with adolescents and young adults (AYA) ages 13-25 with Cystic Fibrosis (CF) or a CF related disorder) to establish feasibility and obtain data necessary to inform a Phase III efficacy trial. AYAs 18 years-old and caregivers of AYAs 13-17 years-old will complete the informed consent process. AYAs 13-17 years-old will be asked to assent to participate in the study. After completion of the baseline study measures and return of actigraphy monitors, staff will notify AYAs of their randomized assignment. AYAs receiving NUDGE will then begin receiving intervention content for 6 months. AYAs randomized to control will receive NUDGE at the conclusion of the Month 3 study visit. Study visits will occur at Months 0, 3, and 6 with staff masked to treatment assignment.

Inclusion Criteria:

1. 13-25 years old
2. Has a verified CF diagnosis or CF-related disorder
3. Medically stable (i.e., FEV1>30%, not experiencing a CF-related exacerbation)
4. Speaks and reads English

Exclusion Criteria:

1. Have a comorbidity limiting PA participation (e.g., neurological condition)
2. Have a significant cognitive impairment that interferes with study completion
3. Have any oxygen, CPAP or BiPAP requirement

Plans to share IPD will need to be discussed with the IRB.