Short mullite fibers were fabricated by adapting the kneading-drying-calcination (KDC) process. The effect of foam forming on the formation of mullite fiber from kaolin via the KDC process, with the addition of a foaming agent, was examined. In the present study, doped sodium phosphates promoted the growth of mullite fiber and the formation of a glass matrix - effects that were ascribed to the P2O5 and Na2O components, respectively, of the sodium phosphates, In particular, the addition of sodium phosphates greatly reduced the treatment time that was required for dissolution of the glass matrix in hydrofluoric acid. The addition of 10 mass% of sodium dihydrogen phosphate and calcination at 1500 degreesC for 10 h were the optimum conditions for a short treatment time and the formation of long fibers.