Iphone6s Plus no storage apps crashing

Apple will only restore your phone, which is the same thing that you can do. Make a current backup of the phone and restore from that backup. That can help clear any space that may be incorrectly identified. See this support document for restoring from backup. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

After that, go to Settings>General>Storage & iCloud Usage, then under storage check Used and Available, and if necessary, go under Manage Storage and you can see what is taking up your space. If you routinely save lots of text messages, messages that contain photos, or lots of mail, then you can be using a lot of storage as well.

The amount of space on a 16GB phone is minimal. The space you describe on iCloud has nothing to do with the amount of storage you have on the iPhone itself. iCloud storage is separate. Go to Settings>General>About and you can see the Capacity of your device and then the Available space on it. If it is out of space, the only thing you can do is delete content on the device. Photos are generally the largest user of space on low capacity devices, like the 16GB phones. You are going to have to manage your storage.