Example about to use deflate functions to write a gzip encoded file in chunks.

<?php

$handler = fopen('/tmp/test.csv', 'w');
$deflateContext = deflate_init(ZLIB_ENCODING_GZIP, ['level' => 9]);

$strings = [
    'Hello, how are you?' . PHP_EOL,
    'I am fine thanks' . PHP_EOL,
    'Hello, how are you?' . PHP_EOL,
];

foreach ($strings as $string) {
    fwrite($handler, deflate_add($deflateContext, $string, ZLIB_NO_FLUSH));
}

fwrite($handler, deflate_add($deflateContext, '', ZLIB_FINISH));
fclose($handler);

echo gzdecode(file_get_contents('/tmp/test.csv'));