Integration with existing site

Hi all, and please excuse me if I’m asking either a common or a stupid question! I did search the forums, and couldn’t find an answer.

I have a client who asked me to build a microsite for a book launch. Having built the site (using the usual PHP, jQuery etc) they have said that they want the content to be fed from their existing Expression Engine CMS…

So, my question is, what is the best way of achieving this (bearing mind I have absolutely no experience in EE, having only encountered it when it was mentioned by the client)? Do I need to rewrite the site in EE? Can I copy my PHP files into EE? Can I just add tags to my existing pages?

Any help gratefully received, as the deadline for the project is extremely tight! 😊

Thanks

Martyn