You're on the right track. For phase transition , use delta S = delta H / T. My guess is you have to assume enthalpy and volume remain constant.
dP/dT=(S2-S1)/(V2-V1) = (H2 - H1)/ T(V2 - V1)
dP = [delta H_trs / delta V] dT /T
P = [delta H_trs / delta V] Ln T + C
C is a const of integration , can be determined by plugging the values of the variables from the given. Remember that density = rho = m / V.