It’s common for Other to be in the 5-10GB range, but if it’s way over 10GB, it has probably grown out of control. You can scroll all the way down to the bottom of the app list to see how much space "System" and "Other" are taking up.
One of the biggest culprits for Other growing out of hand is streaming lots of music and video. When you download video or music from the iTunes store, TV app, or Music app, it’s indexed as Media. But streams have caches used to ensure smooth playback, and those are categorized as Other.
Safari’s caches can start to grow pretty large, too. And if you send tons of texts with images or video, the caches for that can start to fill up a lot of space.
You can’t get rid of Other entirely, but you can sometimes reduce its size.
First, try clearing your Safari caches. Open Settings > Safari and choose Clear History and Website Data. If you have a lot of Safari tabs open on your iPhone, you might want to close most of them, too.
You might also want to change Messages to save fewer old messages. Open Settings, then Messages, and scroll down to the Message History setting. By default, Keep Messages is set to Forever, but you may want to change it to 1 Yearor even 30 Days to reduce the data that the Messages app caches.
Finally, go back to iPhone Storage and look at the apps list. Most of the apps store data that is categorized as Apps, but some will keep caches that are categorized as Other. If, say, the Podcasts app is taking up a couple gigabytes of space, it’s likely mostly cached data. Deleting the app and re-downloding it might put a dent in the Other category.
You can go through your iPhone trying to delete every little cache that could grow the size of Other storage, but if you really want to make it as small as possible, you need to back up your phone and reset it.