why does my iphone 6s only have 16gb phone storage but my ios takes all the space so now my phone doesn't operate

16GB was the base model. 64 GB was the next step up and cost $100 more in the United States. Even back then it was inadequate. The iPhone upped the minimum to 32 GB, but even that can be inadequate if one wants several apps and photos. The size of iOS has gone up over the years, along with the size of apps.

You have an old iPhone with a small amount of storage.

There is nothing you can do about it.

If you need more storage space, buy a newer iPhone with more storage space.

It's possible to clear out some of the "System Data" by backing up to a computer, resetting to factory settings, and restoring from the backup. I can free quite a bit although it tends to come back eventually. A lot of it is garbage collection that doesn't get cleared. The backup doesn't contain all those files and it gets restored without all that junk.

You stated you have nothing on your phone. Anyone here would take that to mean nothing is installed but iOS, and that it is somehow taking up all available space.

Your screen shot shows this isn't true. You have PUBG MOBILE installed, which alone is eating up 2.7 GB of the limited space on your phone. That and the 350 MB in stored photos. Despite that, your phone is NOT full. There's 1.6 GB of free space.

But the issue will always be the same. You only have 16 GB total to work with, of which iOS is taking up about a 1/3 of on its own. You just don't have much storage to work with.

Not possible. I just sold my 6s with 16GB of storage space. iOS 15.x took up about a third of that. You must have other apps or music on it you purchased and installed.