I would recommend a PHP developer to learn a framework but NOT a must!
Learning frameworks would make you have more advantage in the industry compared to someone who decided to stick with vanilla PHP.
There are a lot of job openings out there that required knowledge of frameworks. Is hardly to find a job opening nowadays without frameworks been part of the requirements.
Learn the demanding frameworks in your vicinity. You will find a lot of start-up out there and you would have better changes of securing a job.
And lastly, is to your advantage because there is no harm in trying out something new.