You must have:
a) in your contacts table some field, which allows to assign contact to certain team (one team per contact);
b) or you must have a separate table, where you can assign various contacts to teams (like tblTeamContacts: TeamContactID, TeamID, ContactID where TeamID + ContactID are components of unique index - same contact can be assigned to several teams).
And you have to split the database to front-end and back-end. For every team you create it's own front-end, where instead of whole contacts table only contacts assigned to this team are linked (p.e. you can create for every team a view in backend DB like
Code:
SELECT c.* FROM tblContacts c WHERE TeamID = c.ThisTeamID
or
Code:
SELECT c.* FROM tblContacts INNER JOIN tblTeamContacts tc ON tc.ContactID = c.ContactID WHERE tc.TeamID = ThisTeamID
or
Code:
SELECT c.* FROM tblContacts c WHERE ContactID In (SELECT tc.ContactID FROM tblTeamContacts WHERE tc.TeamID = ThisTeamID)
, and instead of tblContacts you link this view to team front-end).