The words flocks, phlox sound the same but have different meanings and spellings. Why do flocks, phlox sound the same even though they are completely different words?
The answer is simple: flocks, phlox are homophones of the English language.
Plural form of flock.
Third-person singular simple present indicative form of flock.
Any of various North American plants of the genus Phlox, having opposite leaves and flowers with a variously colored salverform corolla.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").