Apologies for the delayed response! In order to take payments with Square, you do have to use the Square app. It's fine to download the app on someone else's iPhone, but keep in mind if you stay logged in to the app, then whomever owns the phone has access to it (and can take a payment, process a refund, etc.) If you go that route, I'd recommend logging out of the app each time you're finished using it to ensure you have control over the activity. Hope that helps, and let us know if you have additional questions!
