  We study ionic microgel suspensions composed of swollen particles for various
single-particle stiffnesses. We measure the osmotic pressure $\pi$ of these
suspensions and show that it is dominated by the contribution of free ions in
solution. As this ionic osmotic pressure depends on the volume fraction of the
suspension $\phi$, we can determine $\phi$ from $\pi$, even at volume fractions
so high that the microgel particles are compressed. We find that the width of
the fluid-solid phase coexistence, measured using $\phi$, is larger than its
hard-sphere value for the stiffer microgels that we study and progressively
decreases for softer microgels. For sufficiently soft microgels, the
suspensions are fluid-like, irrespective of volume fraction. By calculating the
dependence on $\phi$ of the mean volume of a microgel particle, we show that
the behavior of the phase-coexistence width correlates with whether or not the
microgel particles are compressed at the volume fractions corresponding to
fluid-solid coexistence.
