can i buy additional icloud storage for my iphone using my windows laptop

Yes.

Upgrade to iCloud+ - Apple Support

you need iCloud for windows to do it.

Download iCloud for Windows - Apple Support

How to upgrade on your Windows PC

1. Open iCloud for Windows.
2. Click Storage.
3. Click Change Storage Plan.
4. Choose a plan, then click Next.
5. Enter your Apple ID password, then click Buy.

Yes, you need to install the iCloud app to your Windows PC first.