Web development using php provides more opportunities for developers. If you are planning to become a freelance developer, knowing PHP is not enough. You need to acquire some additional skills.
Like I said the PHP knowledge isn’t enough to be a developer. There are high chances of him correcting the mistakes made by designers. On such occasions, you must know HTML and CSS as well. If you are not good at other languages, then the developers more experienced than you in other languages may get the project.