Assuming the book(s) have no DRM, this is what I do:
Connect your phone to your computer and move the epub onto your
Import the epub into Calibre.
Connect your Kobo to your computer.
Use Calibre to load the epub onto your Kobo.
The documented way is to use the Kindle PC app and download the book inside that. The file will end up on your PC and only readable in the Kindle. The current versions download the book as a .kfx file that allows Kindle apps to do more with the data. Older versions downloaded the file as a .azw file.
The USB option does need Kindle hardware. The hardware ...