
I agree with all that has been said. When people say they have a bitch that has never had a phantom I always assume it was mild and the owner never noticed. I once adopted a bitch when her owner died. The family were amazed when I said she'd had a phantom - they said it had never happened before. Yet she had one every single season until I got her spayed. I do think it's pretty normal.
People with multi dog households like mine will often see, after a litter has been born, that other bitches come into milk. If she is feeling forlorn steel yourself against encouraging the phantom to last. Give her extra walks and "jolly" her along. If she produces milk definitely reduce food so she will not have it for long.