OK, so here is an example of how to make this page mobile friendly.... first you add a viewport meta tag to the header:
<meta name="viewport" content="width=device-width, initial-scale=1">
Then you define a mobile css file (attached)
Then add a menu icon to open and close the menu just above your menu UL tag like:
<div id="phoneMenu"><img src="Images/menu_white.png" alt="View Menu" onclick="hideshowmenu()"></div>
I've attached the image you can add to your images folder for the menu icon.