I consider that a mobile “medical” app as a medical device. If you are using that device to collect clinical data it should be considered a medical device. During my capstone project, we programmed an accelerometer and medical monitoring device. This device was connected to the user’s phone which was considered a “medical device”. In your case, you are collecting data of auditory cues. The goal of your project could be to mimic an audiometer, but make it more user friendly. However, you intend to use the phone as “medical device” to collect clinical data. It’s weird because a lot of companies such as apple, google, and samsung are in a dilemma with the FDA. Mainly because they make these phones and and watches that track a biometric data, like heart rate, step counter, how much you sleep, etc. I know the FDA is not as strict when it comes to devices like these, but they will be monitoring them closely.