Audible Question

I am new to using Audible, just signed up and am wondering why it took me so long.

I have a question though....When I go to listen to a book, it says click to download, so I did and then I listed to the book.

Is this book stored somewhere on my phone?  Is it taking up space?  Now that I finished listening to it, can/should I delete it from my phone to free up space?

This may be a silly question, but I don't want my phone clogging up space with downloaded audible files once I am finished with them.  If I can delete the downloaded files after listening to them on my iPhone, how do I remove them?

Thanks for your help.