I deleted two file from my SD card from an app called AK notes. Can deleting files from the SD card harm my phone?
Uh no it's just like deleting a file from your computer...as long as its not anything crucial.
There's nothing stored on the SD card that is CRITICAL to the function of the phone. Some settings, and your personal files are stored out there, but nothing that will keep the phone from operating like it does out of the box.