Which president spoke to astronauts on the Moon by telephone?

On July 20th, 1969, Neil Armstrong became the first man to walk on the surface of the Moon, followed by his colleague Buzz Aldrin several minutes later. An estimated 600 million people watched the moon landing on television. During the moonwalk the astronauts took photographs, gathered soil samples, and raised an American flag. Later they received the first Earth-to-Moon phone call as the president offered the astronauts his congratulations on their work.