I hadn't really put much thought into the cigar until your question, so I am really pleased you asked.

Considering the time period in which "A Doll House" was written, it is probably very unlikely that the author was intentionally applying some Freudian symbolism here, since the play slightly predates most of Freud's publications. But a Freudian critic might argue that the symbol, intentional or not, was likely subconciously dropped into the play. the cigar prop could certainly be subject to a Freudian analysis.

The cigar is a phallic symbol because of it's cylindrical shape and it's being the possession of men. It could symbolize both Torvald's and Dr. Rank's masculinity and/or patriarchal power. Note that Torvald is in possession of an entire box of cigars, very fine ones, in fact. This could indicate his importance as a man, showing that he is in control of many "phallises." Rank, on the other hand, has no cigar of his own. His only power lies in Torvald's hands.

It's interesting that Rank requests the cigar from Torvald, since Rank is secretly in love with his wife, Nora. I suppose Nora's lighting of the cigar for Rank could indicate her ability to excite him sexually. The clipping of the cigar could reflect Rank's inherited syphillis and inability to really act on that attraction. Or it could represent his impending death.

Then again, as Freud once commented, "Sometimes a cigar is only a cigar."

Below are some links that may be helpful.