This is more of a Windows question.
Macs with wifi cards can do it. If you're getting internet through ethernet you can tell the Mac to create its own wifi network and share the internet with that signal.
Then you just sign onto that network with the phone the same as any other wifi.
Whether (and how to) get Windows to do this, I have no idea. I'd suggest googling "internet sharing, windows" to see what you find. The folks here can answer iPhone questions better than Windows questions.