To give you an idea how to do it, take the phone number from file A. I hope it contains only phone numbers. Read that file line by line. See sample code below for line by line reading of file in PERL. Then match the phone number from here in file B and do what you want to do with it. This is one of the ways. There are others ways also to achieve it

my $filename = <yourfile>
while (my $row = <$filename>) {
  chomp $row;
  print "$row\n";
}
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