  We calculate the Higgs-boson mass spectrum and the corresponding mixing of
the Higgs states in the Minimal Supersymmetric Standard Model (MSSM). We assume
a mass-hierarchy with heavy SUSY particles and light Higgs bosons. To
investigate this scenario, we employ an effective-field-theory approach with a
low-energy Two-Higgs-Doublet Model (2HDM) where both Higgs doublets couple to
up- as well as down-type fermions. We perform a one-loop matching of the MSSM
to the 2HDM and evolve the parameters to the low energy scale by exploiting
two-loop renormalization group equations, taking the complex parameters into
account. For the calculation of the pole mass, we compare three different
options: one suitable for large charged Higgs masses, one for low charged Higgs
masses, and one approximation that interpolates between these scenarios. The
phase dependence of the mass of the lightest neutral Higgs boson can be
sizeable, i.e. on the order of a couple of GeV depending on the scenario. In
addition, we discuss the CP composition of the neutral Higgs bosons.
