Եթե քեզ ճիշտ հասկացա ուրեմն սենց
<form action="tester.php" method="post">
<input type="submit" name="submit" value="submit">
</form>

tester.php-ն

<?php
if(isset($_POST['submit'])){
$i=1;
$filename= "test".$i.".html";
while(file_exists("test/$filename")){
$i++;
$filename= "test".$i.".html";
}
$fileCreate = fopen("test/$filename",'w');
if($fileCreate){
echo "Done";
}
}


?>