Can you call a cell phone in the microwave?

Wi-Fi is not just 2.4 Ghz.  It's likely that the test you ran you were actually using a 5Ghz wifi spot, allowing the phone to still get enough signal to operate inside the microwave over a wifi call. Standard microwave leakage on ~2.4ghz would not be enough for decent communication. It however is enough to commonly interfere with 2.4ghz wifi when the microwave is in operation.