Hi there and welcome
On your iPad go the the App Store.
Search for Kindle and download the App onto the iPad.
Then open the App and when asked to register, enter in the same Amazon account you used on the iPhone and all your books will then be available.
If you have any problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.