I have an iPhone 6s with 64 GB of storage and currently over 28 GB are taken up by the 'other' category. I already tried clearing my safari cache, deleting email and message attachments, offloading and deleting apps, and deleting photos and videos. In fact, when I deleted several large message attachments, the messages storage category went down from a little over 2 GB to a little over 1, but the 'other' category increased by about the same amount.
Apple says 'other' is mostly cache files and doesn't need to be manually cleared, but I have no available storage on my phone and and unable to take photos, download more music, etc. 'Other' is taking up almost half of my storage.