Your question is a good one. I hope that I can help answer it.
The requirement or advantage of having a PHD definitely depends on the field of research and the companies or labs that you are interested in. An example is Boeing. It is a private company but has hundreds of PhDs to design the aircraft. National labs, of course, will favor a PHD. Then there are companies like mine where there are only 50 of us in a company of 40,000 people. In our industry, many problems can be solved using common engineering methods and only a few need special tools like the ones that you learn in a PHD program. Keep in mind that my advice is from a fluid dynamics background in mechanical engineering. I am not too familiar with the civil engineering field. However, I work for a construction company and interface with many other companies in the course of a project. Those companies have many civil engineers and I see a similar trend: only a few problems in civil engineering need the tools developed in a graduate program.
I personally wanted a PHD but did not want to go to a National Lab. I wanted to apply my knowledge out in the world as opposed to doing more research. It was definitely harder to find a job but I am very happy with my career. However, I recognize that you do not need a PHD to have a fulfilling career.
There are many students that go out into industry after a Master's and then go back to get their PHD. It can be done but I have heard that it is harder to do. Dig deep and see if you really want the PHD. If so, I recommend to stay in school and finish now.
I suggest that you search out companies and national labs that are doing things that you are interested in. See what qualifications those jobs need. The Federal government and state governments also use civil engineers. Check them out as well. Searching these companies will also help you see if you want to stay on to get a PHD. You may come across a job that you are very interested in and does not need a PHD.
I hope that my point of view helps.