This issue is moved to FAQ : [Using the TAINER as External USB Storage for Your Smartphone]
TAINER can become a battery powered external USB drive. Just connect your smartphone(lightning port or USB typeC port) to the USB Type-C port(Right side) of the TAINER through appropriate USB cable. For Android phone, it is usually Type C to C cable. For iPhone, it is usually USB C to lightning cable. Follow following step to safely connect TAINER to your phone as a self powered external USB drive.
1. Connect your iPhone(lightening or Type-C) through USB cable to the USB type-C port(Located right side) of the TAINER.
2. Turn on the TAINER. You will see computer connection on the LCD
3. Choose [Smartphone] icon. In that mode, TAINER work like battery operated external USB drive and doers not draw power from your iPhone.
4. Now TAINER and your iPhone is connected. Use file browser App of the iPhone to see the contents of the TAINER. Here is the details how you can see it.