The words fishing, phishing sound the same but have different meanings and spellings. Why do fishing, phishing sound the same even though they are completely different words?
The answer is simple: fishing, phishing are homophones of the English language.
The act, occupation, or sport of catching fish.
A place for catching fish.
The act of sending email that falsely claims to be from a legitimate organization. This is usually combined with a threat or request for information: for example, that an account will close, a balance is due, or information is missing from an account. The email will ask the recipient to supply confidential information, such as bank account details, PINs or passwords; these details are then used by the owners of the website to conduct fraud.
The act of circumventing security with an alias.
Present participle of phish.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License 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").