Separate design for phone

Is is possible in WordPress to have a completely separate design for a phone i.e. when the screen is smaller than a certain point? I designed my website for a desktop or tablet. It is not a viable design at all for a phone. Is there even a way to have a separate homepage for a small screen that explains that the website is not designed for phones or even links to a different version which is designed just for phones?

The page I need help with: [log in to see the link]