How to get started with submitting first peer reviewed paper based on PhD?
The procedural parts are pretty simple:


Select the journal you're interested in submitting to.
Read their "Instructions for Authors".
Follow those instructions.


It may sound trite putting it that way, but journals are typically pretty good at being clear about what they want, both in terms of content areas and format &amp; typography.

What you also need to do is identify what you want to take from your PhD, and determine what the "narrative" structure of that material is - a paper that's just a bunch of random things with no through-line is not a great paper.

You may also want to take the time to look at the editorial board of the journal you're interested in, find who is knowledgeable in the topic of your paper and be sure to indicate (in the manner proscribed in the instructions for authors) that you'd like them to be the editor in charge of your paper. A good choice here can help ensure that it's reviewed by the right people for the job.