  We present a measurement of the angle phi1 of the CKM Unitarity Triangle
using time-dependent Dalitz analysis of D -> Ks pi+ pi- decays produced in
neutral B meson decay to a neutral D meson and a light meson (B0bar -> D(*)
h0). The method allows a direct extraction of 2phi1 and, therefore, helps to
resolve the ambiguity between 2phi1 and pi-2phi1 in the measurement of sin
2phi1. We obtain sin 2phi1=0.78+-0.44+-0.22 and cos 2phi1=1.87+0.40+0.22
-0.53-0.32 The sign of cos 2phi1 is determined to be positive at 98.3% C.L.
