I think phillip’s tomb has already been found. I would wonder if it was Alexander’s if he had not been buried in Egypt.
Amphipolis doesn't seem likely for a Macedonian royal burial--it wasn't originally Macedonian (it was founded by the Athenians in 437 and became a Macedonian possession only during the reign of Philip II). It's well to the east of the heartland of the Macedonian kingdom. The historian Thucydides, an Athenian general at the time, was exiled because he failed to prevent the Spartans from taking Amphipolis in the winter of 424/423.