Dwindeling space on my IOS 9.2 iPhone6 – What to do

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Hi All, for those who have an iPhone6 with 16gigs of RAM and are using IOS 9.2, this may be for you.
I continually run out of RAM on my phone.  I have moved all my photos off of the phone to conserve space and cleaned out the deleted picture folder, but I continue to lose space.
I removed apps that I no longer use.
I delete all old iMessages and documents I no longer need.
But I still continually run out of space.
I do not sync my phone to my computer.  Instead I perform updates all through the cloud.
I recently came to a point that I had zero RAM left despite all my efforts to gain back space.   After doing some research, I found
that there are hidden app LOG files and other system areas that were taking up over 5 gigs of space.  A hard reset did not do the trick either and I was reluctant to wipe the phone and start from scratch.
There are applications out there that do not require itunes like Phone Clean, Clean Master and CleanMyPhone to name just three.   Like all new software, I was skeptical and security conscious.
I tried Phone Clean by installing it on my pc, then let it do its thing.  The app found a lot of bloat.  I let it run for about 20 minutes and it finally finished.  And to my surprise, I gained 5.2 gigs back.  Wow, really?  What is Apple doing that we need an external application to perform this clean up???