Phasing is the task or process of determining the parental source of a SNP's alleles. A simpler way to put it, it is the process of trying to determine which DNA came from the mother, and which came from the father. The term is usually applied to types of DNA that recombine, such as autosomal DNA or the X-chromosome. The benefit of phasing is being able to identify which ancestor a segment was inherited from (Ref: isogg.org). This is a simple utility that helps to extract the SNPs of the other parent if one parent and a child is provided.