I was taught that the word postpone was spelled as I just spelled it, but recently I have seen a rise in the spelling postphone (or post phone). At first, I thought it was just a spelling error, but I have begun to see it more and more in official contexts.
Historically, the first spelling is definitely more accurate as you can see in the Online Etymology Dictionary and in Google Ngram. But also notice in the Google Ngram results that recently there has been a slight decline in the use of postpone. If you remove postpone from the Ngram query, you will see that the decline is accompanied by a rise in the use of postphone and post phone.
Are these new spellings becoming an acceptible alternative? Or is this simply a case of the rise in a misspelling accompanying more people having access to publication?
BONUS: The best answer will explain why this variant spelling is so common, if possible.