Format phone number for Turkey (+90) and strip parantheses and spaces.

phone_number_format.js

function () {
  if (!document.querySelector('#telefon') || 0 === document.querySelector('#telefon').value.length) {
    return null;
  }
  var phone = '+90' + document.querySelector('#telefon').value.replace(/[\(|\)|\s]/g,'');
  //+905551234567 -> 13 karakter
  if (13 < phone.length) {
    return null;
  }
  return phone;
}