Hi there,
i can’t see a FA icon in your navigation? I assume you want it where the phone number is.
First off that custom link contains an additional empty <a></a>
tag that you would want to remove before adding the icon:
Then give the menu item a Custom Class of: custom-menu-phone
Then this CSS – you need to change the FA icon unicode where i have commented:
.main-navigation li.custom-menu-phone a:before {
content: '\f095'; /* Change Unicode for FA library */
font-family: FontAwesome;
font-size: 20px;
margin-right: 10px;
}