Although the other answers are correct, this one explains the process in a little more detail. This one uses the GOOGLE BOOKS API.
https://giribhatnagar.wordpress.com/2015/07/12/search-for-books-by-their-isbn/
All you need to do is
1.Create an appropriate HTTP request
2.Send it and Receive the JSON object containing detail about the book
3.Extract the title from the received information
The response you get is in JSON. The code given on the above site is for NODE.js but I'm sure it won't be difficult to reproduce that in PHP(or any other language for that matter).
