以下示例代码可以生成按照id组的PHP序列号：

$users = [
    ['id' => 1, 'name' => 'Alice'],
    ['id' => 1, 'name' => 'Bob'],
    ['id' => 2, 'name' => 'Charlie'],
    ['id' => 2, 'name' => 'David'],
    ['id' => 2, 'name' => 'Emily'],
];

$sequence_numbers_by_group = [];

foreach ($users as $user) {
    $id = $user['id'];
    if (!isset($sequence_numbers_by_group[$id])) {
        $sequence_numbers_by_group[$id] = 0;
    }
    $sequence_numbers_by_group[$id]++;
    $sequence_number = sprintf('%02d', $sequence_numbers_by_group[$id]);
    printf('%d: %s%s' . PHP_EOL, $id, $user['name'], $sequence_number);
}

输出结果：

1: Alice01
1: Bob02
2: Charlie01
2: David02
2: Emily03

以上代码使用了数组和循环结构，在每个id组内维护序列号，同时使用sprintf函数来填充序列号到固定长度。