The identity of the buyer, who bid by phone, has not been revealed.
The bidding in Chesapeake City, Maryland, started at $100,000.
The red phone, which has the Nazi leader’s name engraved on it, was found in his Berlin bunker in 1945.
More than 70 years old, the Siemens rotary telephone is embossed with a swastika and the eagle symbolic of the Third Reich.
Alexander House dubbed the phone – which Hitler received from the Wehrmacht, Nazi Germany’s armed forces – as “arguably the most destructive ‘weapon’ of all time, which sent millions to their deaths”.
It said Hitler used it to give most of his orders during the last two years of World War II.
Soviet soldiers gave it to British officer Sir Ralph Rayner as a souvenir shortly after Germany surrendered.