DISTINCT works on the combination of ALL variables in the query, the variables from A and the variables from B. Whatever is in a.* is not distinct, even though the phone numbers are the same. That's why phone numbers can appear more than once.
If you just want a list of distinct phone numbers use table B and only the variable dcPhoneNumber. However, I suspect that's not what you want either, and so @Sandeep77 it ALWAYS helps (that's ALWAYS) if we know the final result you want, and we don't know that, you haven't told us.
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Paige Miller