He said "Allahu akbar",
Many people from parts of Africa like Senegal and Morocco (predominantly Muslim populations) who come to the United States go into the taxi business, so Frank running into this Muslim cab driver is no coincidence but instead is common in the U.S.
The taxi driver is telling him that no matter how big your problem is, God is greater and He is capable of anything. That’s why he repeats the chorus after he mentions his other problems. But ultimately, prayer doesn’t matter and Frank’s dilemmas are unsolved. He’s basically telling god to put his money where his mouth is.
The taxi driver could also be saying God is greater because he is genuinely concerned for Frank and doesn’t know any other way to help him.
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