Any process in which a virus stops, prevents, or reduces the rate or extent of the phosphorylation of IRF3 (interferon regulatory factor-3), thereby inhibiting IRF3 activation. In response to signaling from RIG-1/MDA-5 receptors, IRF3 is phosphorylated on multiple serine and threonine residues; phosphorylation results in the cytoplasm-to-nucleus translocation of IRF3, DNA binding, and increased transcriptional activation of interferon-encoding genes.