Hello dear,
PHP is a server side scripting language.
It means that it runs on the server only.
when the PHP codes executes on the server, then these codes are converted into browser understandable language i.e HTML, CSS and javascript. So, the PHP codes are converted into HTML format and are send to the clients browser.
ex: PHP code
echo "
this is a paragraph
";
is converted to …
this is a paragraph
and this is send to client’s browser.
So, that’s why we cannot see the PHP codes in the developer mode.