The traveling-wave drift mobility \ensuremath{\mu} was measured in two phosphorus-doped hydrogenated amorphous silicon (a-Si:H) samples which showed at ${T}_{K}$\ensuremath{\approxeq}380 K an upward kink in their conductivity curves and below ${T}_{K}$ a metastable excess conductivity after rapid quenching. No abrupt change in \ensuremath{\mu} occurs at ${T}_{K}$ indicating that the transport process does not change. The quenched state has a somewhat higher \ensuremath{\mu} indicating less disorder. Above 400 K, \ensuremath{\mu} saturates because deep-lying defect states begin to limit the drift mobility.