title_body: What is this lock icon in the lower right corner of my iPhone kindle app?
upvoted_answer: This icon allows you to lock or unlock the screen automatic rotation. The state shown on the screenshot is with the autorotation locked i.e. the screen will not rotate when you tilt the phone.
  
  To unlock or lock the autorotation just tap the icon. It will show up when you tap the lower right corner of the screen.
  
  See for example: How to enable or disable Kindle-app screen rotation