RecruitingClinical trialPhysical Activity Through Health Technology in Axial SpondyloarthritisThe purpose of this study is to find out whether a mobile app called the ExerciseRx app is a practical and helpful way for people with axial spondyloarthritis (axSpA) to receive exercise recommendations as part of their regular rheumatology care. Researchers want to learn: Whether people with axSpA find the ExerciseRx app easy to use and helpful for supporting regular exercise. Whether using the ExerciseRx app leads to improvements in symptoms, physical function, and disease activity compared with usual care. Participants assigned to the ExerciseRx group will use the app to complete guided exercises for 20-30 minutes, four times per week. They will also receive personalized weekly step-count goals to help increase their physical activity. Researchers will compare outcomes between participants using the app and those receiving usual care.