Can php be a substitute for html,css and js?

Answer 1

php is server-side programming language, which by that php files are run on server.
HTML, css, js are client-side languges (frontend) used to mostly display stuff on your site.

So php cant display content without html and css.
But website can work with only html and css.

Answer 2

Simply, the answer is impossible. HTML is obviously necessary, so is CSS and JavaScript. But, PHP cannot replace the importance of JavaScript because JavaScript is becoming popular in app and game development. Again JS is client-side programming language

Answer 3

Not without billions of dollars worth of changes to web standards, browsers and web servers.