"acted as intermediary" is a correct and usable phrase in written English.
You can use it to describe a situation in which someone intervenes between two parties to promote a resolution. For example, "The mediator acted as intermediary between the warring nations in order to bring about a peaceful end to the conflict."
Bernoulli acted as intermediary throughout, and the often candid discussions between Leibniz and Bernoulli provide illuminating background to the correspondence proper.
Using his uncle Bernie Marcus's connections, he acted as intermediary in the purchase of radio station WHOM by Generoso Pope, father of one of Cohn's schoolmates.
But, the jury heard, she gave legal advice to Pryce on contracts with the Mail on Sunday and Sunday Times and acted as intermediary with the Mail on Sunday for Pryce, and the two were in close contact.
Traditionally, among the Otoro there were no political offices, only a special hereditary ritual office that of "chief of the Path," who acted as intermediary in peace negotiations between conflicting parties.
Schwab made a list of the companies to be consolidated, proposed a method of financing, and then acted as intermediary between Morgan and Carnegie in the sale of the latter's operations.
This and other Arabic-language forums hosted discussions on the latest news from Iraq, provided a place for swapping tips on tradecraft, circulated religious justifications for jihad, and acted as intermediary between would-be fighters and their would-be recruiters.
Apparently, shopkeepers allow these street vendors to act as intermediaries as long as they don't physically enter the shop of a competitor.
He said the negotiations went smoothly and took place with district officials, though police officers acted as intermediaries.
Since Mr. Black and Ms. Pratt were supervising, they needed to be at every meeting, and then acted as intermediaries for the bids, which created scheduling and paperwork problems.
The New York Blood Center and the Hutchinson Center acted as intermediaries and translators, censoring references that could identify the donor or recipient at first.
Traditional freight brokers acted as intermediaries to manage the coordination of freight, helping independent drivers or companies match loads with available empty trucks.
