The normal practice is to let the keyboard hide the bottom content.
- Users are used to this convention , they are familiar with touching on the screen to hide the keyboard and touching the keyboard icon ( or any text field , if they are in the middle of some data entry ).
- The user is used to not seeing the bottom part and bringing it up using the same actions above.
A different case
In rare situations , if the content at the bottom of the page is directly related to the text that the user will enter in the text box , hiding the content beneath the key board is a really bad idea.
For Eg:- If the user wants to type in something by reading the content at the bottom-say type a number which is shown at the bottom - , every time user will need to toggle the keyboard which can be irritating for the user.
In such cases alone it will be a better idea to show the entire content, but my personal preference is that you keep such important information at the top of the page unless it is absolutely necessary.
So as a normal and best practice , it is ok to hide the bottom content of the page by keyboard.