Auto Capitalization is enabled by default and it types the first letter of words (according to their place) with capital letter. To turn off and disable auto capitalization on iPhone devices, do as follows:
1. Open the Settings application from the home screen
2. Go the General settings
3. Scroll down to the Keyboard settings and open it.
4. Scroll down again and find the Auto-Capitalization option
5. To disable Auto Capitalization on iPhone, make sure this button is toggled OFF