In the web application and the Outlook sidebar you can see the contact information for the project team.

To see and edit the organization-wide Contact list, you need to go to the Organization Settings page.

Click on Contacts in the lower right of your Home page when logged in on the web.

To edit a contact's information, click on their name.
To edit an organization's information, click on the organization's name (this feature is forthcoming, until then you can only edit the organization's information from a project Team list).

If a contact has left their organization, uncheck the Active checkbox. This will make them inactive on project Teams as well.