The answer would depend entirely on what field the Ph.D. is in and why you are pursuing the degree. A Ph.D. in the Arts and Humanities (English, Art history, etc.) is obtained primarily to continue as a professor and scholar in academia. On the other hand, a Ph.D. in applied physics could be used for academia or to have better grant writing and career advancement opportunities within a private corporation. A Ph.D. in clinical psychology might be solely for private practice as a psychologist. All graduate work involves scholarship, some research, and the development of critical thinking and reasoning, but what form that will take varies significantly by discipline.

Some people are lucky enough to do a Ph.D. and get a nice job that builds upon the skills and knowledge developed during the process. For them, the Ph.D. is a foundation for an excellent career. Alas, these are just a fraction. Most people in most fields don’t enjoy such a luxury. They can find a similar area where the Ph.D. might be treated with respect, but many end up doing something completely different. Many schools’ administration is filled with PhDs that never do anything with their degree. Some people actively leave the Ph.D. off their resume. They find that they get paid more and are treated with more respect if they hide this fact. They know the clients will dismiss them as an arrogant theoretician with little understanding or desire to address real problems.

A Ph.D. helps specifically in the following three ways.

• It shapes our interests helping us to decide what to do next. After the master’s, one doesn’t know what he wants to do. If one is interested in research, he will continue with a Ph.D. Doing a Ph.D. helps one understand the type of work he enjoys steering him in the direction of his career.
• It teaches you a lot and changes your mindset. You are doing in-depth scientific research, taking on the responsibility of your work, dealing with stress, coping with long working days, and taking yourself out of your comfort zone, whether pursuing a complex topic or presenting in front of a large audience, changes you. After your Ph.D., you will have a very different skill set and mindset from what you had after your master’s; this enables you to pursue things you wouldn’t do after studying.
• It opens doors for you. The position you are applying for requires Ph.D. experience and constantly uses the skills acquired during your Ph.D. for your present work. You might not need a Ph.D. to get a specific job, but in many cases, Ph.D. experience can help you to be good at it and grow further.

In short, not all of these are specific to doing a Ph.D.; you may also gain similar changes and benefits from working if you’re driven and motivated.