Sanitizing user input with markdown-like syntax

Since I sanitize all the user-provided string before upload them to the DB, I wanted to give the users the possibility to format text as it happens here on Stack Exchange or on WhatsApp:

• *word* -> bold
• _word_ -> italic

This class contains two functions:

• upload(): is called when the user upload a text and it replaces *word* with <b>word</b>, _word_ with <i>word</i> and \n with <br />
• download(): is called when the user wants to modify the text and it does exactly the opposite; it replaces HTML tags with the custom signs * and _

My questions:

1. Could be this code considered as a real class in the way of thinking or is it just procedural code put into a class?
2. Would you improve it in any way?
3. Do you have any suggestion to write it better?

class txtFormatting {
    private $text;

    function __construct($text)
    {
        $this->text = $text;
    }

    function upload() {
        $this->text = preg_replace('/[ \t]+/', ' ', $this->text); //transforms: 2/+ whitespaces -> 1 whitespace
        $this->text = nl2br($this->text); //transforms: \n -> <br />
        $this->text = preg_replace(array("/\r\n/", "/\n\r/", "/\n/", "/\r/"), '', $this->text); 
        $this->text = explode(' ', $this->text); //each word becomes a value
        $regexAY =
            [
                '/[*]{1}[a-zA-Z0-9]+[*]{1}/' =>
                    [
                        "pattern" => "*",
                        "openTag" => "<b>",
                        "closeTag" => "</b>"
                    ],
                '/[_]{1}[a-zA-Z0-9]+[_]{1}/' =>
                    [
                        "pattern" => "_",
                        "openTag" => "<i>",
                        "closeTag" => "</i>"
                    ]
            ];

        $newText = [];
        foreach ($this->text as $key => $word) {
            foreach ($regexAY as $regex => $value) {
                if (preg_match($regex, $word)) {
                    $pattern = $regexAY[$regex]["pattern"];
                    $openTag = $regexAY[$regex]["openTag"];
                    $closeTag = $regexAY[$regex]["closeTag"];
                    $word = preg_replace('/\\' .$pattern. '(.*?)\\' .$pattern. '/', $openTag. '$1' .$closeTag, $word); // /\*(.*?)\*/ OR /_(.*?)_/
                }
            }
            if ($word !== '') { array_push($newText, $word); }
        }

        return $this->text = implode(' ', $newText);
    }

    function download() {
        /*function br2nl() {
            return preg_replace('/\<br(\s*)?\/?\>/i', "\n", $this->text); // /\<br(\s*)?\/?\>/i
        }*/
        $this->text = preg_replace('/\<br(\s*)?\/?\>/i', "\n", $this->text);
        $this->text = explode(' ', $this->text);
        $regexAY =
            [
                '/<b>[a-zA-Z0-9]+<\/b>/' =>
                    [
                        "pattern" => ["/<b>/", "/<\/b>/"],
                        "replacement" => "*"
                    ],
                '/<i>[a-zA-Z0-9]+<\/i>/' =>
                    [
                        "pattern" => ["/<i>/", "/<\/i>/"],
                        "replacement" => "_"
                    ]
            ];

        $newText = [];
        foreach ($this->text as $key => $word) {
            foreach ($regexAY as $regex => $value) {
                if (preg_match($regex, $word)) {
                    $word = preg_replace($regexAY[$regex]["pattern"], $regexAY[$regex]["replacement"], $word);
                }
            }
            if ($word !== '') { array_push($newText, $word); }
        }

        return $this->text = implode(' ', $newText);
    }
}


$text = "     This _is_ _just_ _a test_
       *text*
       so     _don't_
       consider       it just   *read*
      it";
$a = new txtFormatting($text);
echo $a->upload()."\n";

$text = "This <i>is</i> <i>just</i> _a test_<br /> <b>text</b><br /> so <i>don't</i><br /> consider it just <b>read</b><br /> it";
$b = new txtFormatting($text);
echo $b->download()."\n";