How to make a basic calendar with PHP?

I am a beginner learning PHP and I am trying to make a basic calendar with PHP. Simpele kalender is how it has to look. It has to be with if and/or loops. This is what I have so far:

<?php

$month_start = 'Tue'; 

$number_days = 28; 

// number of rows
$number_rows = $number_days / 7;
    if ($number_days % 7 != 0) {
// number of days
$number_rows = ($number_days / 7) + 1;
}
?>

<table>
<tr>
<th>Mon</th>
<th>Tue</th>
<th>Wed</th>
<th>Thu</th>
<th>Fri</th>
<th>Sat</th>
<th>Sun</th>
</tr>

<?php
for($y = 1; $y <= $number_rows;$y++){
echo "<tr>";
for($i = 1; $i <= $number_days; $i++){
    if($i % 7 != 0){
      echo "<td>". $i . "</td>";
    }
    else{
      echo "<td>". $i . "</td>";
      break;

    }


}
echo "</tr>";
}
?>
</table>
<style>
  table, th, td {
  border: 1px solid black;
  text-align: center;
}
</style>

How do I start on Thursday (beginning of the month) and how can I get the days 1 to 28 in the columns? I made another calendar but that wasn't correct. According to the feedback I got on it, I don't need to use gmdate, cal_days_in_month and mktime. Anyone that can help me go into the right direction?