[Evernoob]

It's hard to say. I published 8 papers before submitting mine - 6 conference and 2 journal. I guess technically you don't really need to publish any, but doing so yields a few key benefits:

a) A conference paper early in the process can get you some really great feedback on your research. You might get to network with some people who are influential or prominent in your field. You may also get greater clarity for the direction you want to take the research.

b) Publishing a few papers means that a lot of the work you'll be submitting in your thesis has already been scrutinised by experts in much the same way that your thesis will be graded. If there are any weaknesses in your work or literature you've overlooked then this should come out in the review process when you submit your papers so you then have time to address the issues. Once published, you have greater certainty that the quality of your work is PhD suitable.

c) You get to put a timestamp on your work in case someone does something extremely similar in the meantime. It's improbable, but it's not impossible. If your ideas are great, the likelihood of this happening increases. If you publish stuff, you can point at your published work and say "look - this idea was mine". This almost sort of happened to me. I took it as reassurance that what I was doing had some merit.

d) Paper writing is similar to thesis writing, albeit on a much smaller scale. You still have to review the literature, present your work, evaluate it properly and do all the necessary comparisons to other existing stuff. If you can get a small paper published it's great practice for what you'll ultimately have to do for the thesis.