  Superconducting fluctuations (SF) in SmFeAsO$_{0.8}$F$_{0.2}$ (characterized
by superconducting transition temperature $T_{c} \simeq 52.3$ K) are
investigated by means of isothermal high-resolution dc magnetization
measurements. The diamagnetic response to magnetic fields up to 1 T above
$T_{c}$ is similar to what previously reported for underdoped cuprate
superconductors and it can be justified in terms of metastable superconducting
islands at non-zero order parameter lacking of long-range coherence because of
strong phase fluctuations. In the high-field regime ($H \gtrsim 1.5$ T) scaling
arguments predicted on the basis of the Ginzburg-Landau theory of conventional
SF are found to be applicable, at variance with what observed in the low-field
regime. This fact enlightens that two different phenomena are simultaneously
present in the fluctuating diamagnetism, namely the phase SF of novel character
and the conventional SF. High magnetic fields (1.5 T $\lesssim H \ll H_{c2}$)
are found to suppress the former while leaving unaltered the latter one.
