  We explore the connection between the stiffness of an hadronic equation of
state (EoS) with a sharp phase transition to quark matter to its tidal
deformability. For this we employ a hadronic relativistic mean field model with
a parameterized effective nucleon mass to vary the stiffness in conjunction
with a constant speed of sound EoS for quark matter. We compute multiple
scenarios with phase transitions according to the four possible cases of a
hybrid star EoS with a stable second branch. We demonstrate at the example of
GW170817 how the effective nucleon mass can be constrained by using
gravitational wave data. We find, that certain values of the effective nucleon
mass are incompatible with GW170817 and a phase transition simultaneously. By
using the recent NICER measurements of J0030+0451 at the $1\sigma$ level we
constrain our results further and find that strong phase transitions with a
visible jump in the mass-radius relation are ruled out at densities below 1.7
times saturation density.
