The view of a PhD from inside and from outside is different. From the outside, a PhD is an accomplishment that anoints individuals to be experts who knows everything. The view is a little less exciting from the inside.
In the computer science field, a PhD will teach you three things: how to become an expert, well-informed in a very narrow field and how to research.
The Ph.D. program in Computer Science allows students to become experts in technical areas of computer science. By reading and researching, PhD students contribute via their own research and publications. PhD students work with world-class experts in their field.
If you pursue a PhD, you will learn a lot about something small and contribute significantly to a given field. For example, if you research on operating systems, you might become an expert in hyper-threading performance for a specific model and brand of processor. You may not know anything significant about memory management, networking and file systems, etc.
Research is the most important part of a PhD. Student learns what a significant contribution is, how to select research topic, how to write it up, and where to submit it. In most universities, a PhD research project includes a period of research that includes the submission of a thesis, and its subsequent oral examination, as well as a series of reports.