  Particle tracking and displacement covariance matrix techniques are employed
to investigate the phonon dispersion relations of two-dimensional colloidal
glasses composed of soft, thermoresponsive microgel particles whose
temperature-sensitive size permits \textit{in situ} variation of particle
packing fraction. Bulk, $B$, and shear, $G$, moduli of the colloidal glasses
are extracted from the dispersion relations as a function of packing fraction,
and variation of the ratio $G/B$ with packing fraction is found to agree
quantitatively with predictions for jammed packings of frictional soft
particles. In addition, $G$ and $B$ individually agree with numerical
predictions for frictional particles. This remarkable level of agreement
enabled us to extract an energy scale for the inter-particle interaction from
the individual elastic constants and to derive an approximate estimate for the
inter-particle friction coefficient.
