You cannot report the difference in proportions as your phi coefficient because it is only a quick-and-dirty estimate to be used before you actually calculate the real value.

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The phi coefficient is a measure of association for two binary variables, providing a value between -1 and 1 that indicates the strength and direction of the association. It is not simply the difference in proportions, which would not account for the distribution of outcomes across the categories in the same way or provide a standardized measure of association.

You Cannot Report the Difference in Proportions as Your Phi