switchToFrame
if the page have othe frame, you can use switchToFrame(frameName) or switchToFrame(framePosition) to exchange it.Other similar methods are switchToChildFrame(),switchToFocusedFrame,switchToMainFrame and switchToParentFrame
Examples
var webPage = require('webpage');
var page = webPage.create();
page.open('http://www.sample.com',function(status){
if(status!== 'success'){
console.log('Unable to access network');
}else{
page.switchToFrame('framwName/framwPosition');
console.log(page.frameContent);
phantom.exit();
}
});