Hi what i am trying to do is not to get the webpage as
page.open(url);
but to set a string that has already been retrieved as the page response
Yes, and it is as easy as assigning to page.content. It is usually also worth setting a page.url (as otherwise you might hit cross-domain issues if doing anything with Ajax, SSE, etc.), and the setContent
function is helpful to do both those steps in one go. Here is the basic example:
var page = require('webpage').create();
page.setContent("<html><head><style>body{background:#fff;text:#000;}</style><title>Test#1</title></head><body><h1>Test #1</h1><p>Something</p></body></html>","http://localhost/imaginary/file1.html");
console.log(page.plainText);
page.render("test.png");
phantom.exit();
So call page.setContent with the "previously retrieved page response" that you have.