Dynamics of the defect, phase defect 'type-P' formed on Si(100) surface dimer rows, was studied at 6 K by scanning tunneling microscopy. Pair creation and annihilation of the type-P defects were observed clearly. It was observed that step edges and dimer vacancy defects work as sources and absorbers of the type-p defects. Interaction between the phase defects existing on the adjacent dimer rows was very weak at 6 K compared to that observed at ∼100 K. This resulted in the comparable structural change between c(4×2) and p(2×2) arrangements; dynamics of the type-P defects looked almost equivalent in c(4×2) and p(2×2) arrangements at 6 K. With consideration of the interaction between dimers, the observed characteristic properties were considered to be related to the temperature dependence of the dimer interactions, in addition to the phenomena of the ordinary order-disorder phase transition between c(4×2)+p(2×2) and unique c(4×2) structures.