I recently started working for a web firm as a freelancer taking my hobby of coding in PHP to a career level, and since then I have been overwhelmed by the amount of work that needs to be done within short time frames.

The problem isn't being able to do what is asked, but being able to do it all as quickly as is needed of me. I never used any PHP frameworks, but if I started using one, would that speed up the entire development process? If so, how drastically?

Also which framework would be best for my purpose?

If it matters, what I do is mostly build back end cms's and tie that with front end functionality for small business client sites.