The lattice dynamics in an array of 56 nm diameter Bi2Te3 nanowires embedded in a self-ordered amorphous alumina membrane were investigated microscopically using Te-125 nuclear inelastic scattering. The element specific density of phonon states is measured on nanowires in two perpendicular orientations and the speed of sound is extracted. Combined high energy synchrotron radiation diffraction and transmission electron microscopy was carried out on the same sample and the crystallinity was investigated. The nanowires grow almost perpendicular to the c-axis, partly with twinning. The average speed of sound in the 56 nm diameter Bi2Te3 nanowires is similar to 7\% smaller with respect to bulk Bi2Te3 and a decrease in the macroscopic lattice thermal conductivity by similar to 13\% due to nanostructuration and to the reduced speed of sound is predicted.