You can decode type codes using the mdb_type_name() function:

<?php

    $db = mdb_open("test.mdb");

    for ($i = 1; $i <= 13; $i++) {
        echo "Type $i is ".mdb_type_name($db, $i)."\n";
    }

?> 
Type 1 is Boolean
Type 2 is Byte
Type 3 is Integer
Type 4 is Long Integer
Type 5 is Currency
Type 6 is Single
Type 7 is Double
Type 8 is DateTime (Short)
Type 9 is Unknown 0x09
Type 10 is Text
Type 11 is OLE
Type 12 is Memo/Hyperlink
Type 13 is Unknown 0x0d