1. What kind of information you will find in each section of a research paper in your field.
2. What are the major research programs in your field and where they disagree.
3. How to identify where a paper's author stands with respect to the major disagreements in your field.
4. How to decide that a paper isn't worth your time without reading all of it.
5. How do you write a research paper?
6. How do you decide what research to do? (This decision will often be made for you for the first couple of years.)
7. Where you stand with respect to the major disagreements in your field.
8. How to synthesize half a decade's work into a realtively brief document.
Notably, these skills don't help you do any of the following:
1. Manage a research group in an academic setting.
2. Teach undergraduates.
3. Manage people in industry.
You might pick up applicable skills along the way, but these are incidental. Any specific skill, any particular knowledge, can be obtained without getting a Ph.D. The Ph.D. teaches what you need to know to advance the field.
I'd like to return for a second to talk about teaching undergraduates. It's a very important thing to do. Ph.D. training ought to include pedagogy. Standards for university instruction are shockingly low, and professors are rarely held to account for failing to teach the material well, especially at R1 institutions. However this comment is not about what you should learn, but about what you'll actually learn in a Ph.D. program if you decide to enroll tomorrow.