Phenotype mixing is a form of interaction between two virus particles, each of which holds its own unique genetic material. The two particles "share" coat proteins, therefore each has a similar assortment of identifying surface proteins, while having different genetic material. In other words; nongenetic interaction in which virus particles released from a cell that is infected with two different viruses have components from both the infecting agents, but with a genome from one of them.
References
Phenotype mixing Wikipedia(Text) CC BY-SA