Writing - or writing up?

I've been working on my PhD for about 2 weeks now. I've bought some subject-related books (about care, AI, and the robotic revolution) and I've bought 3 books about PhD research. The books I've bought are:

• How to write a thesis - Rowena Murray 
• Authoring a PhD - Patrick Dunleavy
• Writing your thesis - Paul Oliver

...and of course I've chatted to numerous students who are currently studying for - or about to start studying for - their doctorate. And something which has come up both in the books and when chatting to other students is this thing called "writing up". I admit I haven't read the above books from cover to cover, so it's possible that they will solve the mystery for me. But I am, at the moment, at a loss: I just don't see what people mean by 'writing up' as though it is something fundamentally different from writing or editing. I've started to wonder whether others work in a different (better?) way than the way I work.

Typically, this is how I would write something; it's the approach I've used to write textbooks, it's how I wrote all my MA essays, including the dissertation, and it's the approach I intend to use to write my PhD thesis:

1. Have an idea and make some handwritten notes in my notebook
2. Make more substantial notes / a plan on the computer (eg a 500 word plan of the steps my argument will take)
3. Read some relevant articles and make notes on the PDFs
4. Transfer some quotes / arguments to my essay to support my argument or as something to argue against (and edit my argument so as to agree or disagree with the literature)
5. Refine my question and argument by writing more, and deleting less useful parts
6. Repeat steps 3-5 a few times
7. Write introduction and conclusion
8. Decide that my essay is almost finished, and proofread for typos, formatting, and other small errors
9. Repeat step 8 several times until I can read through it without making any corrections
10. It's finished!

Which, if any, of these steps is 'writing up'? It seems to me that none of them are. Sure, some steps involve writing, but the study texts and PhD students talk as though 'writing up' is something distinct from mere writing. For example, I've heard PhD students say things like "I'm in my third year now, so I've done all the work; now I'm just doing the writing up" or "I'm allowing myself six months for writing up" and I find myself wondering: if they 'write up' in their final year, what have been doing the rest of the time? Reading I presume, but then does this mean that they read for 2.5 years without doing any writing, and then do all their writing in one go? Who knows?

Perhaps one day in my PhD journey I'll fathom the difference
between writing and editing, and writing 'up'.

I'm two weeks in and I have written about 3000 words so far. It's not amazing; it's not polished; it will probably be unrecognisable if it makes it into the finished thesis, having gone through several edits and re-edits - or it might not make it into the finished thesis at all. But I have done some writing (and some reading) and I will keep adding to my writing, improving what I've done and adding clarifications and detail, until it is done. If that's how I work (and it is how I work!) then it seems that I won't be doing any 'writing up' at all. 

Perhaps 'writing up' is more relevant to non-philosophical subjects (xphi notwithstanding), where a PhD involves a literature review, an explanation of methodology, results gathered and interpreted, and then conclusions drawn? Perhaps in such disciplines one spends a lot of time reading and explaining literature (without much argument of their own), collecting and analysing data, and then the 'writing up' is something that can (only?) be done afterwards, to draw together all these different threads and create a finished piece?

The thing is that I've dabbled in xphi (a piece of MA coursework I wrote about trustworthiness) and I was writing throughout. I wrote my argument and methodology, and a tentative interpretation of early results as I went along: I didn't just gather the data and then 'write up' my work as a separate process. This meant that once all the results were in, I only needed to edit and tweak my interpretation of the results rather than write it from scratch, meaning that there was no distinct time when I 'wrote up' my essay. I guess maybe my approach wasn't best practice, or maybe there are some disciplines that simply can't do things the way I did my Xphi study?

So it seems to me that there are only these two possibilities:

EITHER:

• Writing a Philosophy thesis is fundamentally different from other PhD theses

OR

• The way I work is fundamentally different from the way other students work

Perhaps I am displaying a woeful naïvety, and over the next year or two I'll have some sort of 'writing up epiphany' whereupon I'll realise what writing up entails... or perhaps I will do things my own way, only to discover all too late that my work is shoddy because I merely wrote it and edited it and proofread it, but I never wrote it 'up'. Because despite my having pondered this for the last week or so, I still cannot fathom how 'writing up' is a thing in itself, distinct from writing and editing.