Using Babel with PhantomJS, evaluate function being executed in browser context doesn't have access to helper functions - phantomjs

Question

I'm trying to use PhantomJS with a script that's compiled by Babel from ES6 to ES5.
For some of the features, Babel puts in some helper functions at the end of the file (like _asyncToGenerator and _typeof) to evaluate the code.
But in Phantom, there's a function evaluate(function(){…}) which is executed in the browser context, so it doesn't have access to those helper functions babel puts in.
Ex, if I have a code:
var page = require('webpage').create();
page.open(url, function(status) {
var title = page.evaluate(function() {
typeof(document.title);
});
});
It compiles to
var page = require('webpage').create();
page.open(url, function(status) {
var title = page.evaluate(function Executed_in_Browser_Context() {
_typeof(document.title);
});
});
function _typeof(obj) { return obj && typeof Symbol !== "undefined" && obj.constructor === Symbol ? "symbol" : typeof obj; }
Notice the typeof has been changed to _typeof (for some feature involving ES6 Symbols)
Here, the function Executed_in_Browser_Context is executed in browser context, and so it doesn't have access to the function _typeof defined in the file at the bottom. And so it results in error
Can't find variable: _typeof
How to solve this?
I tried copying the _typeof inside Executed_in_Browser_Context (pre-compilation) but then upon compiling, Babel sees that and thinks that it may be some other function that I have in my code, and just renames its own to _typeof2 resulting in same error.