contact.js

// Kahit tanggalin mo na din yung pattern since nag JS validation na naman
<input type="text" name="contact" id="contact" maxlength=11 onchange="validateContact()">

function validateContact() {
  // Palitan mo nalang yung id sa getElementById

  var contactLength = document.getElementById('contact').value.length;
  var submitButton = document.getElementById('theSubmit');
  
  if(contactLength == 7 || contactLength == 11) {
    submitButton.disabled = false;
  } else {
    alert('Invalid number length');
    submitButton.disabled = true;
  }
}