20Φ0 means the year "two thousand and ten." It happens when you are writing down the date and ten years of rote influence you to write the numbers two, zero, and zero as the first three digits of the written year. You attempt to correct the mistake by superimposing a "1" over the second zero, hence the resultingly embarrassing Phi-in-the-date.
by HankAaronCopland January 6, 2010