Sounds like you need a third table, maybe called AssociatedCompanies. You would add two reference fields, one to Contacts and one to Companies. Then you would modify the Contacts reference field to Composite = Yes, making it a child of Contacts. You don't have to, but it sounds like it should be a child.

If you know you only have 2 or 3 Companies per Contact you can always make another reference filed to Companies. But this method is not as flexible as the third table.

You need a model like this (it's German and a different topic, but the same method). I have houses and facility managers. Every facility manager can manage several houses, but a house can be managed by more than one facility manager

Haus = house, Verwalter = manager, Hausverwaltung = facility management.

Facility management (= Hausverwaltung) looks like this