Pdostatement::fetch_array()

Question

I’m having a problem at a input of the kind Select (follows the excerpt below). I am using version 7.0 of PHP and as DBMS Postgresql. I tried to use the function pg_fetch_array but it was unsuccessful, someone has an idea of what might be wrong?

<?php
    $consulta = "SELECT * FROM atividades";
    $query = $db->db->query("SELECT * FROM atividades");
?>
 <select>
          <?php 
            echo "<select name='descricao'>";
              while($cont = $query->fetch_array()) {
                echo "<option value='".$cont["id"]."'>".$cont["descricao"]."</option>";
              }
            echo "</select>";
          ?>
      </select>

This is the return specified by var_dump($query);