In underdoped cuprates, T-c is thought to be determined by Cooper pair phas
e fluctuations because of the small superfluid density n(s). Experimentally
, T-c is found to scale with n(s). The fluctuation-exchange approximation (
FLEX) in its standard form fails to predict this behavior of T-c since it d
oes not include phase fluctuations. We therefore extend the FLEX to include
them selfconsistently. We present results for T-c[n(s),x], where x is the
doping.