I'm halfway through my PhD in theoretical physics and so far, I have never written a paper on my own. At best I wrote short parts for an article published with my advisor. I am currently taking part in an international collaboration and we decided that I should try and write our paper. I spend about 2 weeks on it and barely reached 2.5 pages (two-column APS style). I sent my work to the advisor and he said that "it is not good". We only spoke shortly on a phone, so I expect him to give me some more feedback. However, he has given me feedback before and it hasn't been all that helpful. His main advice is for me to be more verbose which I just don't know how to do.
How can I learn to write scientific publications? Any tips? Training ideas? Sources I can follow? I just feel that in a quite short time I should become an "independent researcher" and that should include the ability to write a paper on my own. With the current pace, I definitely won't achieve that by the end of my PhD and that gives me a lot of anxiety.
I'm not an English native speaker. I'm not sure if that matters but wanted to clarify.