Why not just sample from your phone into the OP-1F? Using the Lightning to USB-C cable, you’ll get a digital stream directly in.
Seems like many people get stuck on the idea of a USB disk mode, dragging and dropping files. The OP-1 is literally setup to handle sampling things quickly.
That app was originally made for the OP-1 and it’s third party so you may be victim to bugs and slow updates/fixes.