You'll also need CSS for page layout and know about SQL and relational data modeling for storing data. And if you want your websites to do anything (as opposed to just static pages), you should know the basics of JavaScript and JQuery.
That will be enough to develop your own websites and is a great place to start. However, if you want someone to hire you, it might be hard to get a job with just that basic minimum. Here are some other things I'd be looking for in a full-stack PHP developer:
- at least one PHP MVC (model view controller) framework like Laravel, Symphony, etc.
- CMS (content management system) experience with Drupal, WordPress, Joomla, etc.
- experience in object-oriented programming
- MySQL or Postgres database administration
- linux command line
- basic Apache web server administration
- XML, JSON
- REST APIs
- IDE (integrated development environment) experience like Eclipse
- JavaScript MVC frameworks like AngularJS or Backbone
- Bootstrap
- Git
If you are doing this with the hopes of getting a job, start browsing job listings now. For the jobs that look interesting to you, see what technologies they tend to list. That will give you a good idea what to focus on. You might even find that the jobs you're most interested in don't want PHP developers but Python, Java, etc.