How to disable something at a certain screen size

Hey,

I recently put a phone number in the header of my website, but now whenever I’m on mobile template or even on an iPad where the screen is smaller, the phone number will go behind the header logo. Is there anyway to disable the phone number at a certain screen size, so it doesn’t overlap on something.

If you need a visual of what I mean, go to http://www.fastiphonefix.com and reduce the screen size, and you’ll see how the phone number will end up overlapping the text.

Thanks!