Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/TextData.php
public static function FIXEDFORMAT($value, $decimals = 2, $no_commas = false)
    {
        $value = Functions::flattenSingleValue($value);
        $decimals = Functions::flattenSingleValue($decimals);
        $no_commas = Functions::flattenSingleValue($no_commas);

        // Validate parameters
        if (!is_numeric($value) || !is_numeric($decimals)) {
            return Functions::NAN();
        }
        $decimals = floor($decimals);

        $valueResult = round($value, $decimals);
        if ($decimals < 0) {
            $decimals = 0;
        }
        if (!$no_commas) {
            $valueResult = number_format($valueResult, $decimals);
        }

        return (string) $valueResult;
    }
public static function FIXEDFORMAT($value, $decimals = 2, $no_commas = false)
    {
        $value = Functions::flattenSingleValue($value);
        $decimals = Functions::flattenSingleValue($decimals);
        $no_commas = Functions::flattenSingleValue($no_commas);

        // Validate parameters
        if (!is_numeric($value) || !is_numeric($decimals)) {
            return Functions::NAN();
        }
        $decimals = floor($decimals);

        $valueResult = round($value, $decimals);
        if ($decimals < 0) {
            $decimals = 0;
        }
        if (!$no_commas) {
            $valueResult = number_format($valueResult, $decimals);
        }

        return (string) $valueResult;
    }
FIXEDFORMAT.

@param mixed $value Value to check
@param int $decimals
@param bool $no_commas

@return string