What is “others” in iPhone storage ?

Some of it is system data. Maybe caching. But with that much storage there isn't really that much benefit. The system will make much of that available if needed.

If it really bothers you, it's possible to make it go down by restoring to factory condition then restoring from a backup. I've found that it cleans up iOS devices and reduces the "Other" category. But eventually you'll be back where you started. And if you've got that much spare capacity it's not really something that's going to affect anything.