The words graft, graphed sound the same but have different meanings and spellings. Why do graft, graphed sound the same even though they are completely different words?
The answer is simple: graft, graphed are homophones of the English language.
A plant produced by such union.
To unite (a shoot or bud) with a growing plant by insertion or by placing in close contact.
To join (a plant or plants) by such union.
To transplant or implant (living tissue, for example) surgically into a bodily part to replace a damaged part or compensate for a defect.
Simple past tense and past participle of graph.
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").