The words freak, phreak sound the same but have different meanings and spellings. Why do freak, phreak sound the same even though they are completely different words?
The answer is simple: freak, phreak are homophones of the English language.
A thing or occurrence that is markedly unusual or irregular: A freak of nature produced the midsummer snow.
An abnormally formed organism, especially a person or animal regarded as a curiosity or monstrosity.
A sudden capricious turn of mind; a whim: "The freaks of the psyche can no more be explained than the Devil” ( Maurice Collis).
Slang A drug user or addict: a speed freak.
Slang To manipulate a telephone system illicitly to allow one to make calls without paying for them.
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").