What's the difference between PHA and FA in Hindi Alphabets

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I have seen Hindi letters pronounced PHA and FA. For example Phool is different from Fool. Actually what's the difference between these two? Is there any difference in written script between these two letters? In Malayalam we don't have PHA.....but we have BHA and FA similar to Hindi. I want to know what's this PHA :whistle: :whistle: :S :S