Multiple forms with one button for 2 different functions

Question

can anyone help me, I don't know how to make a button that can be used for the same 2 forms & add php action on one page. I've seen some of the other questions but that didn't solve my problem

<form name="form2" id="form2" method="post" action="">
                          <div class="form-group">
                            <label for="name">Your Name</label>
                            <input type="text" class="form-control" id="name" required placeholder="Enter Your Name" name="name">
                          </div>
                          <div class="form-group">
                            <label for="notlp">Your Phone Number</label>
                            <input type="tel" class="form-control" id="notlp" required placeholder="Enter Your Phone Number" name="notlp">
                          </div>
                          <input type="hidden" name="cust" value="Toko A">
                          <div class="form-group" style="text-align: center;">
                        </form>

 <form id="loginForm" class="form-horizontal" role="form" action="<?php echo $linkloginonly; ?>" method="post">
                            <input type="hidden" name="dst" value="<?php echo $linkorig; ?>"/>
                            <input type="hidden" name="popup" value="true"/>

 
             
                                    <input type="hidden" value="cust" class="form-control input-lg" id="inputLogin" name="username"
                                           placeholder="Login" autofocus required>
                                    <input type="hidden" value="cust" class="form-control input-lg" id="inputPassword" name="password"
                                           placeholder="Password" required>
                                    <div class="align-content-center" style="text-align-center" > </div>
                                    <button disabled id="btn" type="submit" class="btn btn-primary btn-block btn-lg">OK</button>
                              
                        </form>

this for php file https://docs.google.com/document/d/1BJvMovZHH_My2leeE2djWiOYLIOuObrQQN01paawqgE/edit?usp=sharing

script

<script type="text/javascript" src="js/md5.js"></script>
<script type="text/javascript">
<!--
    function doLogin() {
    <?php if(strlen($chapid) < 1) echo "return true;n"; ?>
    document.sendin.username.value = document.login.username.value;
    document.sendin.password.value = hexMD5('<?php echo $chapid; ?>' + document.login.password.value + '<?php echo $chapchallenge; ?>');
    document.sendin.submit();
    return false;
    }
//-->
</script>

<script>
  document.getElementById('btn').onclick = function() {
  var x = document.forms["form2"]["name"].value;
  var y = document.forms["form2"]["notlp"].value;
  if (x == "") {
    alert("Name must be filled out");
    return false;
  } else (y == "") {
    alert("Phone Number must be filled out");
    return false;
  } 
}
</script>

<script>
    getElementById('btn') = function(){
    document.getElementById("form2").submit('SubmitButton');
}
</script>