I would also suggest investigating the M.A. programs in philosophy that have a good track record of helping people get into top PhD programs. However, I'd also add that majoring in philosophy is not a requirement for admission to most PhD programs, and many strong graduate students in philosophy have majored in other fields. Whether you are competitive for the better PhD programs depends largely on your letters of recommendation, GRE scores, and, as already noted, your writing sample.
It might not disqualify you at some programs, but it will certainly count against you at most. The writing sample is the primary way of distinguishing applicants' philosophical talents, at least once they have been narrowed down using other criteria (such as coursework in philosophy and grades, letters--though for the competitive candidates, they tend to be equally gushing--and perhaps GRE). A 5-page sample is unlikely to provide evidence that you can develop an argument responding to a particular position that you have adequately and charitably explained. (Of course, Gettier's famous paper is quite short!)
I say all this with empathy--I was a philosophy minor (not major) and did not have a good, long piece of writing to submit when I applied to grad school. I had to use a mediocre, long piece, and was lucky to be accepted in the few places I was. But that was (too) many years ago when the competition was a little less fierce. I would try to work with one of your professors to develop one of your short papers into something more substantial (12-18 pages).
(On the other hand, people should NOT submit pieces longer than 20 pages.)
You sound like you have a clear picture of the costs and benefits of getting a PhD in philosophy. You should continue to talk about it with your mentors in the field. You also sound like you might benefit from getting an MA (full disclosure: I teach at Georgia State in Atlanta, a terminal MA program). It would give you more background in philosophy and give you a better sense about whether you are interested in going on to get the PhD and whether you have the right skills, background, and demeanor to devote your life to professional philosophy. And if you do have those interests and abilities, an MA will enhance them and situate you to get into a better PhD program (the market is rough, so if you want a job where you have the time and encouragement to do research, you will be much better off going to a highly regarded PhD program). It will be difficult to be an active part of the field (publishing and presenting your work) without a PhD and an institutional affiliation. It can be done but you also risk being perceived as a "crank" even if you aren't one, and more importantly, you probably won't be able to devote the time and effort to the issues to be on top of the literature.
If you do decide to pursue an MA or PhD, I encourage you to do a lot of research about relevant programs, looking at their websites, their faculty member's research expertise, their placement record, and the perception of their quality (which is quantified on the Philosophical Gourmet Report, to be used as one source of information among many).
Well, your question suggestions a modus tollens argument:
If one is an amazing philosopher, then one could not fall for something so stupid. Since Levy did fall for it, he must not be an amazing philosopher.
That seems to be the conclusion drawn here. However, I know nothing about this philosopher (except that he's trying to take down Kant!), so I don't know if there is some explanation for this bizarre behavior that might salvage the 'amazing' label.
1. you talk to the philosophy professors at your school and ask them lots of questions. Hopefully, there is someone that who has a good sense of what it takes to get into grad school in philosophy, to succeed, and to get a job.
2. you explore websites at some PhD and MA programs. There is also some useful information at http://www.philosophicalgourmet.com/
3. if you remain interested (as I hope you do!), you consider putting off graduation one semester and taking more philosophy courses. I fear that only one course in philosophy will take you off the radar at many programs (I suspect it would take a lot--e.g., very high GRE and GPA--to get some PhD programs to consider you, when they have so many applicants that are philosophy majors or even have MAs in philosophy).
4. you consider applying to MA programs in philosophy to strengthen your background (though it will still help to have more courses in philosophy to get in to MA programs).
5. you will need a polished writing sample with a philosophical argument in it and you will need at least three letters of recommendation (and I think at least 2 of them need to be from philosophers).
None of this is meant to dissuade you, and your outside reading will be helpful (it's just a bit hard to make it evident in an application).
I hope this helps. And good luck!