Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Statistical.php
public static function QUARTILE(...$args)
    {
        $aArgs = Functions::flattenArray($args);

        // Calculate
        $entry = floor(array_pop($aArgs));

        if ((is_numeric($entry)) && (!is_string($entry))) {
            $entry /= 4;
            if (($entry < 0) || ($entry > 1)) {
                return Functions::NAN();
            }

            return self::PERCENTILE($aArgs, $entry);
        }

        return Functions::VALUE();
    }
public static function QUARTILE(...$args)
    {
        $aArgs = Functions::flattenArray($args);

        // Calculate
        $entry = floor(array_pop($aArgs));

        if ((is_numeric($entry)) && (!is_string($entry))) {
            $entry /= 4;
            if (($entry < 0) || ($entry > 1)) {
                return Functions::NAN();
            }

            return self::PERCENTILE($aArgs, $entry);
        }

        return Functions::VALUE();
    }
QUARTILE.

Returns the quartile of a data set.

Excel Function:
QUARTILE(value1[,value2[, ...]],entry)

@category Statistical Functions

@param mixed $args Data values
@param int $entry Quartile value in the range 1..3, inclusive.

@return float