Maybe you should clean up your iPhone space despite you think you have not much apps on iPhone.Here are some tips for you.
1. Go to Settings > Safari > Clear History & Clear Cookies & Data. This takes up a surprising amount of space if it isn't cleared on occasion.
2. Go to Settings > General > Usage > Here, you'll see a list of apps that are using your space sorted from the app taking the most space down to the app taking up the least space. Right from here you can remove apps that are killing your storage.
3. I would recommend backing up photos and videos to your computer regularly than deleting them from your phone. Plus you can limit music to what you actually listen to regularly.
4. If you want know more how to free up storage on iphone . You can have a try.I hope it is useful for you.