The phrase "acted mainly" is correct and usable in written English.
It can be used to describe the primary manner or focus of someone's actions in a specific context.
Example: "In the play, the actor acted mainly as a comedic relief, bringing laughter to the audience."
Alternatives: "primarily acted" or "mostly performed".
On BP, Mr. Podesta has acted mainly as a liaison between Congressional investigators and the embattled company.
While the movement acted mainly through mass demonstrations, permitting only 'symbolic counter-violence against objects', its rage against the American war in Vietnam ('genocide') was incandescent.
Both in the Niagara Movement and in the NAACP, Du Bois acted mainly as an integrationist, but his thinking always exhibited, to varying degrees, separatist-nationalist tendencies.
In China, Jesuit missionaries acted mainly as agents of European education and culture (e.g., astronomy, mathematics, and technology) in their positions as civil servants of the court.
But nearly half of the voters surveyed, and a substantial part of the Democrats, said Mr. Obama had acted mainly because he thought it would help him politically, rather than because he had serious disagreements with his former pastor.
The judges said the soldier, Anat Kam, 24, who served in the office of the commander of the Central Command, which is responsible for the West Bank, had acted mainly out of ideological motives.
There has been marked improvement since then, so it acts mainly as a "backstop".
Is he, as Dowell sometimes appears to want to insist, a "sentimentalist" who acts mainly out of love and compassion?
No longer happy to act mainly as middlemen, many have wanted a slice of the action themselves.
These substances act mainly through mechanisms that result in the release of catecholamines from their storage areas in nerve terminals.
Though by now she had married Ronald Reagan, she continued to act, mainly concentrating on television, and appearing with her husband in episodes of the Ford Television Theatre and General Electric Theater series.
