Just a note regarding the size of Oracle  NUMBERS will always return 22 as their "size".
This seems to be an Oracle feature. The rest of the documentation is in bug5156.(PHP 5, PHP 7, PHP 8, PECL OCI8 >= 1.1.0)
oci_field_size — Retourne la taille d'un champ Oracle
   Retourne la taille du champ column Oracle .
  
statementUn identifiant de requête OCI valide.
columnPeut être l'index du champ (l'indexation commence à 1) ou le nom du champ.
   Retourne la taille du champ field en octets, ou false si une erreur survient
  
Exemple #1 Exemple avec oci_field_size()
<?php
// Création de la table avec :
//   CREATE TABLE mytab (number_col NUMBER, varchar2_col varchar2(1), 
//                       clob_col CLOB, date_col DATE);
$conn = oci_connect("hr", "hrpwd", "localhost/XE");
if (!$conn) {
    $m = oci_error();
    trigger_error(htmlentities($m['message']), E_USER_ERROR);
}
$stid = oci_parse($conn, "SELECT * FROM mytab");
oci_execute($stid, OCI_DESCRIBE_ONLY); // Utilisation de OCI_DESCRIBE_ONLY si aucune ligne n'est récupérée
echo "<table border=\"1\">\n";
echo "<tr>";
echo "<th>Name</th>";
echo "<th>Type</th>";
echo "<th>Length</th>";
echo "</tr>\n";
$ncols = oci_num_fields($stid);
for ($i = 1; $i <= $ncols; $i++) {
    $column_name  = oci_field_name($stid, $i);
    $column_type  = oci_field_type($stid, $i);
    $column_size  = oci_field_size($stid, $i);
    echo "<tr>";
    echo "<td>$column_name</td>";
    echo "<td>$column_type</td>";
    echo "<td>$column_size</td>";
    echo "</tr>\n";
}
echo "</table>\n";
// Affiche :
//    Name           Type       Length
//    NUMBER_COL    NUMBER        22
//    VARCHAR2_COL  VARCHAR2       1
//    CLOB_COL      CLOB        4000
//    DATE_COL      DATE           7
oci_free_statement($stid);
oci_close($conn);
?>
Just a note regarding the size of Oracle  NUMBERS will always return 22 as their "size".
This seems to be an Oracle feature. The rest of the documentation is in bug5156.