CLICK HERE to see the article which states that the phrase "cellar door" is the most euphonious phrase in the English language.
Henry James wrote: "Summer afternoon--summer afternoon--to me those have been the two most beautiful words in the English language."
I think that most people would say that "I love you" is the most euphonious phrase in our language.
Mona Lisa included this: "I know you dislike Woody Allen, but you MUST use his quote." The quote: "The best words in the English language are not 'I love you', but 'It's benign'!"
One of my favorite songs from childhood was Playmate (listen here) which includes the line "slide down my cellar door". See the cellar door which is reminiscent of my childhood. It NEVER looked or sounded "beautiful" to me.