Online Clipboard
Share a clipboard between iPhone and Windows
The one combination neither Apple nor Microsoft built for: an iPhone in your hand and a Windows PC on the desk.
Why neither side helps you
Apple's Universal Clipboard is part of Continuity and works only between Apple devices signed in to the same account. Windows is simply not part of that picture.
Microsoft's clipboard sync goes the other way: it covers Windows and Android, through a Microsoft account. The iPhone is not supported for clipboard sync, and iCloud for Windows syncs photos and files rather than what you last copied.
So there is no setting to switch on. Every working route goes through something in the middle.
The usual workarounds
Emailing yourself works but is slow and clutters the mailbox. Messenger apps work if you run the same one on both, and will recompress images. Cloud storage works but wants an account on both ends and turns a ten-second job into a sync.
All three share one flaw: they were built for something else, and moving a snippet of text through them is the least comfortable thing they do.
A shared board in the browser
Both devices have a browser, and that is enough. Open Online Clipboard on the Windows PC, and a board appears with a QR code. Scan it with the iPhone camera and both are looking at the same board.
From there it goes in both directions: paste on the iPhone and it shows up on the PC, drop a file on the PC and download it on the phone. Text entries have a copy button that puts them straight into the system clipboard.
No Apple ID, no Microsoft account, nothing installed on either side — which also makes this the route that works on a work machine where you are not an administrator.
In short: There is no built-in bridge between iPhone and Windows. Anything that works goes through a third party — pick one that needs no account and deletes itself.