Have a look at the Long Term Projects module at https://www.odoo.com/apps/trunk/project_long_term/

I haven't used it but it seems to include the features you are looking for. In the Team Planning view you can assign people to different projects and view them in a gantt view or in a calendar. If you have to define multiple single dates for many people, it might take a while, but still it should be a good option.

EDIT:

I think I understood your problem now. From what I gather, the Project Phases are, well, phases of the project. They could be something like "Collecting requirements", "Development" and "Maintenance" (or Sprint 1, Sprint 2, etc). Each phase has their own Tasks and the tasks are in a certain Stage (analysis, design, test, blocked, finished, etc). Then there are Resources, but I couldn't find any connection between the other entities and resources, so maybe that's just some kind of additional feature.

Since a task is bound to a single phase, you cannot use phases to schedule the working time or place. I believe you have to introduce a new concept of 'Work Scheduling' or 'Work Assignment' to deal with your problem. A work assignment would have at least a many2many relation to tasks, a many2one or many2many relation to the project worker, starting & ending dates and the work location (possibly a customer in model res.partner, many2one).

Thanks for you answer. I've looked at the long term projects but I'm a bit puzzled by the introduction of phases. The problem is that I can draw plannings but only for the phases which have to be defined by project. What I, idealy, want, is to create a project with different stages (Analysis, Design, Implementation, ...) and then create tasks within each stage. I would then like to have a planning showing the resources based on the tasks that they have to work on. Any idea how should I approach openerp to do that? Thank you in advance!