how to validate in javascript to accept phonenumber only from 8-10 digits and also should not start with digit 1

function email()
{
  if (document.getElementById("<%=txtEmail.ClientID%>").value=="")
      {
                 alert("Please enter your Email ID");
                 document.getElementById("<%=txtEmail.ClientID%>").focus();
                 return false;
      }

  
    var emailPat = /^(\".*\"|[A-Za-z]\w*)@(\[\d{1,3}(\.\d{1,3}){3}]|[A-Za-z]\w*(\.[A-Za-z]\w*)+)$/;
     var emailid=document.getElementById("<%=txtEmail.ClientID%>").value;
     var matchArray = emailid.match(emailPat);
     if (matchArray == null)
    {
               alert("Your email address seems incorrect. Please try again.");
               document.getElementById("<%=txtEmail.ClientID%>").focus();
               return false;
    }
    }