You can achieve your objective all in one page using javascript, php code is not needed here. See example code below:
<!DOCTYPE html>
<html>
<body>
<form id="loginForm" style="display:block">
<p>this is login form</p>
<input type="button" id='reset' value="Reset password" onclick='changeForm(this)' />
</form>
<form id="resetForm" style="display:none">
<p>this is reset form</p>
<input type="button" id='login' value="Goto login" onclick='changeForm(this)' />
</form>
<script>
function changeForm(e){
var whichButton = e.id;
if (whichButton == 'reset'){
document.getElementById('loginForm').style.display="none";
document.getElementById('resetForm').style.display="block";
} else {
document.getElementById('loginForm').style.display="block";
document.getElementById('resetForm').style.display="none"; }
}
</script>
</body>
</html>