Most of the modern Phal hybrids don't breed well or at all because many of them are aneuploid-that is, they don't have the normal number of chromosomes. These modern hybrids are produced without regard for their chromosome count, so cannot reproduce by seed. It is unlikely that you are doing anything wrong. Mericloning itself doesn't make the plant sterile. The best thing is to get a plant that is known to be a good breeder and experiment with that.