JavaScript phone number validation

PhoneNums.js

function FormatPhone(ThePhone){
  if (ThePhone.length >= 9){
    ThePhone = ThePhone.replace(/\(/gi,"");
    ThePhone = ThePhone.replace(/\)/gi,"");
    ThePhone = ThePhone.replace(/-/gi,"");
    ThePhone = ThePhone.replace(/\ /gi,"");
    return ThePhone;
  } else {
    return "invalid";
} }

function NoChrs(Field){
  ChangedPage = true;
  AllowedChrs = "";
  if (Field == "Phone"){
    AllowedChrs = "().-";
  }
  tempArr = document.getElementById(Field).value.split("");
  for (i=0;i<tempArr.length;i++){
    if ((isNaN(parseFloat(tempArr[i]))) && (AllowedChrs.indexOf(tempArr[i]) == -1)){
      tempArr[i] = "";
  } }
  document.getElementById(Field).value = tempArr.join("");
}