  Magnetic flux structure on the surface of EuFe$_2$(As$\rm_{1-x}$P$\rm_x$)$_2$
single crystals with nearly optimal phosphorus doping levels $x=0.20$, and
$x=0.21$ is studied by low-temperature magnetic force microscopy and decoration
with ferromagnetic nanoparticles. The studies are performed in a broad
temperature range. It is shown that the single crystal with $x=0.21$ in the
temperature range between the critical temperatures $T_{\rm SC}=22$ K and
$T_{\rm C}=17.7$ K of the superconducting and ferromagnetic phase transitions,
respectively, has the vortex structure of a frozen magnetic flux, typical for
type-II superconductors. The magnetic domain structure is observed in the
superconducting state below $T_{\rm C}$. The nature of this structure is
discussed.
