The words few, phew sound the same but have different meanings and spellings. Why do few, phew sound the same even though they are completely different words?
The answer is simple: few, phew are homophones of the English language.
Amounting to or consisting of a small number: one of my few bad habits.
Being more than one but indefinitely small in number: bowled a few strings.
An indefinitely small number of persons or things: A few of the books have torn jackets.
An exclusive or limited number: the discerning few; the fortunate few.
Used to express relief, fatigue, surprise, or disgust.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").