Phone Link is Microsoft’s late and closed source alternative to KDE Connect. It requires you sign in to a Microsoft Account for it to work.
This means all the transactions between your phone and your PC are monitored and sucked up by Microsoft.
How does KDE work in regards to sharing content between computer and phone?
That would be one of KDE Connects’ main functions, yes. It makes sharing any kind of file (photos, videos, whatever) easy.
You can also share the content of your clipboard from your desktop to your phone and vice versa. So you would copy, say, a web address on your desktop, and you would be able to paste it into your web browser on your phone immediately.