Look at the pictures. Are the two pictures: a. a minimal pair, b. homophones, c. whatever?
Ok, best answer comes from Teresa Bestwick on twitter - "oronyms". These are two phrases which sound the same due to features of connected speech. Although I guess this pair of oronyms is less than perfect, because the "p" would be aspirated in "pies" but not "spies". So you'd be able to hear the difference if you were listening really closely. Here's a post from blogger Heather Johnson on oronyms. The importance of oronyms in listening is highlighted from this example from Jason Anderson: he said, "All that I'm after today is ..." and his student understood, "All the time after today is...". In other words, "that I'm" = "the time". There are far more homophonous stretches of sound in natural speech than we usually realise!