Some artists not appearing on iPhone after PC transfer

Could they be showing under compilations or various artists? See Grouping tracks into albums.

tt2

Are you using Artist and Album Artist consistently? Have you attempted to merge different values with a common sort value? What is the first missing artist? Can you see anything that might explain the issue? Obscure issue covered in the Multiple tags (MP3 files only) section of Repair security permissions for iTunes for Windows.

tt2

I'm using iCloud Music library rather than syncing my devices these days, but if I was seeing the same thing I would clear the music off the device and then sync a single playlist to the device starting with just say one artist, then say half the A's then all of them, and so on, each time seeing that everything that I've added has shown up where I expect it to, or going back to see what changes are required to fix things that don't. Grouping tracks into albums and Multiple tags (MP3 files only) are the summary of all of the significant factors that I've found over 10 years of using iTunes and Apple devices. I tweak every new album I import to iTunes with these factors in mind so I never have any problems when the tracks make it to my devices.

tt2

It depends on where the files are before you add them to iTunes. See Make a split library portable for some background on the shape of the iTunes library. If you put all of your files inside the media folder before you add them to iTunes, or make use of the Automatically Add to iTunes folder, then there is no duplication to worry about, plus your library is in the right shape to backup and move around when needed, and you have all of the content in the library ready to restore to your device as and when needed.

tt2

You should to add your content to iTunes, and then add content that is in iTunes to your device. Although since iTunes 12.7 you're allowed to add apps, tones, iBooks, and PDFs directly from Windows Explorer/Finder to the device that isn't how you're supposed to add music. If it works at all expect to get unexpected results.

tt2