In DN8 we are now using jQuery.
If you need to rely on jQuery, you need to register your function/callback with a dnOnLoad() call.
You can use the "JQuery" variable to reference JQuery, or use our variable/shortcut "$dnj" (which we use in case JQuery has been included multiple times). You should not use "$" as this conflicts with prototype.
var phNumEl = $dnj(".dn-phone-number"); //or JQuery(".dn-phone-number");