@Pesto-ThePest man… I gotta tell you that I laughed after reading your question not because it was dumb or anything like that. But because I was in a similar situation than you are right now, I applied for any program I could find, got accepted, hated, dropped out, and now I am applying for 2 other programs but now being way more selective. So you are more than definitely right by making that question!!
In a few words, a Ph.D. program will teach you the skills how to do research. Period. Your field of psychology is very close to mine in Organizational Development which drinks from psychology and sociology so I believe we can talk a little bit in detail.
How do you show proven skills that you know to do research? You do research. Simple as that. Will it be one experiment? Two experiments? You and only you (hopefully with the help of your advisor) will have to decide about that according to what new theory you want to support.
What kind of work will you do during the Ph.D. program? That’s up to each program to decide. I am applying to two programs. In one of them, I will have to write a review, a study, and a dissertation. On the other, I will have to develop a tool for practice, a study, and a dissertation. So there is no specific guideline for this. My suggestion is for you to reach out to the students of each program you are considering and also to the faculty over there.
Another suggestion I would give you is to talk with the students about their routine inside the program, how is their interact with the faculty, and the culture over there. It is very easy for Ph.D. programs to have a toxic culture and rest assured that this can even be possible in psychological departments. For instance, I experienced that in a Leadership department. Leadership!
I also recommend reading the work from the faculty or the supervisor you are interested in applying to. Ph.D. level supervision is very specific so it does not help to apply for any program if they are not specialized in the topic you are interested in. Having similarities might help but you will have to show in your research proposal / personal statement that relates to your topic to the point you are able to convince the admissions committee.
Additionally, I would suggest you consider a master’s degree before the Ph.D. That would be a good way to get in touch with research before putting yourself through this mental health meatgrinder.
I hope I have helped answer some of your doubts!!