Fine structures were observed in the tunneling conductance of a sintered Bi 2223-SnO2 junction. The structures are weaker than those of a single crystalline Bi2212. They correspond to the Raman spectrum of Bi2223 and approximately to the phonon density of states of Bi2212. The structures must therefore be phonon structures, and phonons may contribute substantially to high Tc superconductivity. Multiphonon structures are scarcely discernible. Hence we propose a new model, in place of the prior multiphonon model, to explain the rapid increase in Tc with the CuO2 layer number. 2Δ (21 K)=68±4 meV in Tc=98±5 K. 2Δ (0)/kBTc is 8.1±0.9. The temperature dependence of the gap was also observed and discussed.