is data stored in iphone encrypted by default? according to the following website:
http://www.makeuseof.com/tag/stop-thieves-recovering-data-factory-reset/

it is stated that iphones encrypt all data stored in them:
The iOS operating system on Apple iPhones and iPads has to deal with a similar problem. To ensure a user’s data can be quickly and completely wiped when the device is factory reset, it has a trick up its sleeve. All data on the device is encrypted by default using the hardware encryption feature. When you choose to set up encryption, the device is protected with your own encryption key. Even if you never set up encryption, the files are stored on the device in encrypted form so any bits of deleted files appear as random gibberish on the device’s storage after it’s reset. The data can’t be recovered.

im confused.

is all data stored in iphones encrypted by default?
specifically iphone 5s
Yes, the data is encrypted by default. However it is not "secure" in the sense that if you do not set up a sufficiently good pass code, it is easy to read the data if you have access to the phone.