Do I need a !DOCTYPE declaration in a php file with html?

Question

I have a php file with my website content in it. The file needs to be .php because i get some variables first and then use it later in the website content. Like this example

Answer 1

When they contain embedded HTML, it's better to think of .php files as regular HTML files which the server has been instructed to scan for dynamic (PHP) code.

A valid !DOCTYPE declaration is still necessary for the document to be semantic.