[elinkser]

Yes, even html works well in KOReader(font resizing, fulltext reflow, search, hyperlinks) without conversion to another format.
My suggestion of conversion of a web page to PDF on your phone has the advantage of not requiring a desktop while still conserving images (edit - of course with a desktop images could also be conserved by saving "complete" web page in firefox and converting to epub in calibre OR transferring the image folder along with the html file to the Kobo).
KOReader reflow even allows font resizing and text reflow for PDFs, but my test of the fulltext search did not work properly with the converted PDF document.(Edit - unless you turn off reflow - not ideal if you do alot of searches.)
Also if you save an html file on your phone, you can still webserve it to the kobo, but you have to rename it temporarily to a .pdf extension or else the kobo web browser will open the .html file instead of downloading it. You want to download it as a ".pdf" and then use the KOReader filemanager to rename the file to end in ".html", if you want to use KOReader (and not the Kobo web browser) as the fileviewer.
Of course if you do your browsing on the desktop and not your phone, it's probably easier to just plug in your kobo and transfer the file!