Change url encoding of objects to html characters?

I used the jquery function serialize()for the form, made an ajax call, and used php to process the form.

I have textarea in the form where the user type uses spaces and line breaks. I can access the values ​​using $ _POST, but it does not interpret line breaks in html tags <br/ >. Is there a function that converts the string, translates the urlencoded string into tags <br/>and other html tags? Or is everything already decoded by the time I access it using $ _POST, that I can’t do anything about it?