Some people, including myself have pointed out that Shotwell Photo Manager is not able to import images and video files from some Android phones. The error reported is:

Unable to fetch previews from the camera:
Could not claim the USB device (-53)

Here is my workaround:

1. Close Shotwell
2. Connect your phone to your computer using a USB cable
3. Check the USB connection type on your phone
   • Make sure you are connected as a "media device (MTP)", not a "camera device (PTP)"

     

4. Open your file manager
5. Unmount the phone by clicking on the button highlighted in the following image:

6. Now open Shotwell
7. Click on your phone's name under "Cameras"
   • You should see any images or videos on your phone
8. Import using the "Import All" or "Import Selected" options