I don’t know that they could move a portal once it was established, so that would have required him to actually move into the portal. Maybe you could make one and then collapse it real fast on them. Using a portal as an offensive weapon had not been seen, so it’s likely there are reasons why it wouldn’t work.
But the redirecting of incoming fire was established by Strange and Wong, and I was disappointed to not see a callback to that. Would have been amusing at least, to see the bombardment being redirected up at Thanos’s ship.