The usual formula is to "add to the knowledge of humanity" or some such thing. It isn't ALWAYS a research publication, this is true. But that's the most frequent thing by far. And most usually reported on in a thesis. Usually there are some other requirements that must also be fulfilled, such as a residency requirement, often but not always 3 years. There can also be requirements to take certain number or types of course work and pass it with some particular level. There can be lots of other requirements, depending on the degree. A psychology degree, for example, probably has clinical work attached.
Some times there are also limits. For example, some schools will have a time limit on how long you can take to do a PhD before they start to ease you to the door. There may be other limits.
Such details are likely to be somewhat different from university to university, even from one department to another in the same university. The requirements for your PhD are quite probably set out in some sort of document at your school. Probably there is some kind of charter or guide or some such that will tell you such details.
If you are concerned, the thing to do is probably ask one of the administrative assistant staff persons for some guidance. Maybe the head of your department's graduate work has a secretary (or it may be that some other job title is used). Or your department may have an admin. Or maybe the department of grad studies at your university.
They are good people to know and be friendly with in any regard. They usually know all the non-academic details and can give you the "inside" information about what you need to do, what you should do, and what you should avoid doing. Often more accurately than the profs, since the admins usually wind up doing the gritty details the profs are too lazy to do.
The admins will also be able to get you lots of other good information like when to apply for various things, what you need as far as documentation, how to fill in forms, etc. etc.