Poly(aryloxy)phosphazenes emerge as an important class of hybrid polymers for a whole range of potential applications. To date, however, little is known about the detailed reaction mechanisms during preparation. This draws a great deal of attention for developing well-defined and well-controllable synthesis methods. In this paper, poly(dichlorophosphazene) (PDCP) has been successfully synthesized, and subsequent reaction with sodium phenoxide or phenol in the presence of K2CO3 can produce poly(bis(phenoxy)phosphazene) (PBPP). To elucidate the issues of branching and cross-linking, focuses have been placed on the change of various reaction conditions, in terms of concentration, temperature, time, solvent, catalysis, etc. The product polymers were examined using the techniques of 31P and 13C NMR, GPC, XPS, and FT-IR, in order to characterize the structural defects, in particular, branching and unwanted substitutions, such as addition of water molecules or oxidation of the phosphorus atoms on the backbone of the polymers. This work sheds light on the tailor design of poly(aryloxy)phosphazenes and other polyphosphazenes with more uniform and controllable structures.