Q: iphone6S 128gb memory is suddenly full

Hi a-ikkin,

Thanks for using the Apple Support Communities!

I understand that more storage is being used on your iPhone than you would expect. To begin troubleshooting this situation, I would recommend using the instructions in the following article to look and see what applications are taking up space.

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

Once you are able to narrow down where your iPhone’s storage is being used, you can start to remove data, if you choose, to free up some space. The next article was written to give advice for freeing up space prior to an update, but the steps should still prove useful to you. 

If you need more space for an iOS update - Apple Support

Best!