I want to perform a function if the height of the page is over a certain pixel value. Is this possible?
No... PHP generates the output before the code is rendered. Your best option would be something in JavaScript.
Not with PHP. Javascript can get at least the screen resolution as well as the current browser window resolution. Get those values into PHP and take it from there. Not a JS wizz so can't help further than this...
I'll do some javascript searches, but I haven't done much with it before, other than look at scripts others have made, but this doesn't sound all that difficult. If you want to move this topic shawn, i'll understand.