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There is no such requirement in EU anti-trust law. Any deal that restricts the freedom of contract with a third party is illegal.

> I thought violating anti-competitive laws required one party to cross-subsidize, use advantages in one field/area to drive out competition in another

No. See Article 102 TFEU [1]. Abuse of a dominant market position in order to distort or avoid competition can take many forms.

[1] https://en.wikipedia.org/wiki/Article_102_of_the_Treaty_on_t...

> Would Microsoft be fined for reaching an exclusive agreement with Nokia to sell their only Windows Phones ?

Probably not, because Windows Phones are in no way dominant so there's no abuse of a dominant market position there.

Though I don't know for sure how the EU would view it.

There are lots of tactics that constitute an abuse of a dominant position. Cross-subsidizing isn't one of the worst.