Relationship between photos on iPhone and photos in iCloud

[czissman]

My fiance has an iPhone 6 running IOS 9.2

In "All Photos", her phone shows 17,000+ photos.

When looking at her phone from a Windows computer, we see four DCIM (?) folders containing a total of just over 2,000 pictures.

When looking at her iCloud account, we see the 17,000+ photos.

QUESTIONS
Since we can only see about 2,500 pictures when viewing her phone from a notebook, are there really 17,000+ pictures on her phone, or are 14,500 of them in iCloud only but visible from her phone?

Assuming those 17,000+ pictures are both on her phone and in iCloud (synced as opposed to backed-up), then deleting a picture from her phone would also delete it from iCloud. Is this the case?

Assuming that deleting pictures from her phone will also delete them from iCloud, what's the preferred manner of backing them up permanently before deleting them from her phone and thus iCloud?

Thanks for your help!

Bonus question: Why can she only see 2,000 or so pictures when accessing her phone from a notebook?

 

[J. A.]

What you see in "All Photos" is in iCloud as well. You are right by assuming that the images are synced to iCloud, and not backed up. So if she removes an image from her device, it will also be deleted in iCloud. The 17,000+ photos actually are on her device.

There are several ways to store the photos somewhere else.

It's possible to save them to online storage, such as Dropbox, OneDrive, Google and others. The three I mentioned can upload images from her device automatically, so she won't have to do this manually, since it would need quite some time, with the amount of photos on her iPhone.
There's also Flickr, which offers 1 TB of online storage for free. All you need to do, is keep the images private, if she doesn't want to show them in public. Flickr also can upload images automatically.

Usually, when you connect your iPhone to a Windows computer, you should find the iPhone as camera (Not in iTunes), and it's possible that way to import photos to the computer.