WUP doesn’t define much of how to work in this phase, since its philosophy is to let everybody do in which he’s best. However, there are a couple of things that should be mentioned.

The conceptual phase does not require a specific team. Depending on the company, business scope or customer, the people that create a concept are chosen.

Marketeers and developers don't mix

Usually marketeers are involved. Their advantage is that they can create concepts without bothering about technical stuff; but their advantage is also their disadvantage. A lot of web projects are spoiled because business marketers and application development hardly mix.

To prevent from this, it is important to address the technical scope of a concept in an early stage. This means that at least a member of the technical department should be incorporated in the conceptual process, to verify whether it is technically possible to build an application that fits the concept. Don’t sign or promise anything until this is verified!

The customer rules (literally)

In the conceptual phase, it is as important as in the later phases to remember that the customer for whom the concept is created knows his business best. So when thinking of a business concept, communication with the customer is key.

Forget the web stuff

The other thing is: don’t try to speak of buttons, navigation or any web stuff like that in a business concept. It’s supposed to be a concept, not an application design.
Wait with the nifty details until the Analysis Phase starts, and let developers define them: they know best how to do that. If you don’t stick to the big picture, for sure the customer will get falsely informed, because the details will change in the process anyway. Usually, the best business concepts can be described in just a couple of written pages.
Obviously, the end of the conceptual phase requires the commitment of a project sponsor.