There could be many reasons for the cross not taking. A common one with modern Phal. hybrids is they may have unusual ploidy like 3N. If this is the case, it is likely they won't breed even with a selfing. Also, it could be related to how long the flowers have been open. A friend of mine says that, in general, flowers are most fertile 2-3 days after opening. If the flowers have been open for a long period of time, the chance of successful fertilization goes down. Sometimes crosses don't take for unknown reasons.