Hi schroochesmom,
Welcome to the Apple Support Communities!
I understand that you are trying to import all of your photos from your iPhone to your Windows computer, but not all of them are being recognized for importing. Did you take all 900 of these photos using your iPhone’s camera or where they synced onto your iPhone from a computer?
The attached article below does explain the process for importing photos from your iPhone to your computer. If all of the photos were taken with the iPhone’s camera, you should be able to import all of them.
Import photos and videos from your iPhone, iPad, or iPod touch to your Mac or Windows PC - Apple Support
You can import only photo and video content taken with the built-in camera or captured on the device. You can't import photo or video content synced from iTunes.
Best regards,
Joe