The concluding half of the Dr. Phosphorus story is featured in Detective 470 (June 1977), by Englehart, Simonson and Milgrom.
Batman goes to discuss Dr. Phosphorus with Jim Gordon, who is sharing a hospital room with Alfred. With Gordon incapacitated, the city council, under Boss Thorne, push through a bill outlawing Batman.
Meanwhile, Dr. Phosphorus continues his reign of terror, wiping out the entire audience at a rock concert.
Aware that Dr. Phosphorus is using the abandoned nuclear plant as his base, but incapable of approaching it subtly, Bruce goes the other way, and hosts a huge party on his yacht, using that to sail near the plant. Boss Thorne is there, but so is a new character, Silver St. Cloud. She doesn’t do much aside from flirt with Bruce in this story, but she’ll be back.
With a specially insulated costume, Bruce swims away from the yacht and confronts Phosphorus. They battle, and it’s not so much that Batman beats him, as that Phosphorus causes his own defeat, as his hands burn though the railings and he falls into the reactor, setting off an explosion.
Dr. Phosphorus returns in a couple of years, in the pages of Batman.