It's not so basic question at all. There is no strict rule on what takes up most time in the development cycle. It completely depends on the type of and the magnitude of the game. Generally there are roles that should be filled. These do not necessarily translate to the number of people as especially in small projects people tend to have multiple roles. I started writing, but http://www.cigame.com/different-roles-in-game-development.html contains pretty much what I would have written about different roles and some more. Of course not all of them are always necessary.
For a very small game all the roles may be managed by single person. For a little bigger game it seems common enough that there are project leader/architect/main developer and game designer/artist/musician. For bigger games all these will simply be given to different people of trade.
Usually at most about 4-5 people per manager is a maximum they can decently manage. For bigger games there is often a hierarchy of managers. It seems for larger games number of artists is what grows most. Having an orchestra make the music probably drives up musicians count. Still, there are usually few developers working on the base-system. The rest of the developers are more game designers and in content scripting and generation.