SD card full, lots of space on phone but can't use

[BertG]

You can check the status of your SD-card under Settings

• Storage & USB

If your SD-card is formated as external storage it is headed “Portable Storage”, otherwise it should be listed as “Internal Storage” or most likely just calculated as such.

You really should think twice before formatting it as internal storage, as this can cause problems, e.g. if your phone breaks. You than can not simply take out the Card and transfer all the data to your computer, as the card is not accessible.
Before making a decision, you might want to take a look here:

A little guide to... using SD cards

Android 6 introduced new options for using an SD card in your phone. When you format an SD card or insert a new SD card, you’ll have two options: Internal/phone/adopted storage or external/portable storage. The option that most closely matches older Android versions is the external option. There are a couple of things to take into account when choosing which option works best for you: TL;DR: Formatting as internal will allow you to store apps on it and have it encrypted with the system interna…