Iphone 6 storage issue

Check your storage on your iPhone, iPad, and iPod touch - Apple Support

Use iTunes to check the storage on your iOS device

1. Open iTunes on your computer.
2. Connect your device to your computer.
3. In iTunes, select your device. You'll see a bar that shows how much storage your iOS content uses, divided by content type.
4. Hover your mouse over a content type, like Other or Apps, to find more information:
   

Here is a list of the types of content on your iOS device, and what each type includes:

• Audio: Songs, audio podcasts, audiobooks, voice memos, and ringtones
• Video: Movies, music videos, and TV shows
• Photos: Camera Roll content, Photo Stream, and Photo Library
• Apps: Installed apps
• Books: iBooks books and PDF files
• Documents & Data: Safari Offline Reading List, files created within apps, and app content like contacts, calendars, messages, and emails (and their attachments)
• Other: Settings, Siri voices, system data, and cached files

More about cached files in "Other" iOS storage

Cached files are created when streaming or viewing content like music, videos, and photos. When you stream music or video, that content is stored as cached files on your iOS device. iTunes categorizes cached music, videos, and photos as Other instead of actual songs, videos, or photos.

If storage amounts on an iOS device differ from what you see reported in iTunes

Since iTunes categorizes cached files as Other, reported usage for Music or Videos might differ. To view usage on your iOS device, go to Settings > General > Usage > Manage Storage.

I got a IPhone 6s with 64gigs onboard what I have done is use a Scandisk wireless (wi fi) device

and use it as a external storage only thing you can do you can download the app at

scandisk if you can't find the app contact scandisk and they will give you link to it

make sure you ask for the IPhone app.

I use a SanDisk wireless flashdrive "wi fi" device Been using

it for months it is a "external storage device" you can find the app at the

Apple app Store. In the search box on top type "wireless" enter

and it should show a app called "SanDisk Connect Wireless Media".

If it does no come up go to SanDisk.com contact SanDisk and ask for

the IPhone app. ask for the link to their app make sure you ask for the Apple

app.

Hope this helps