  We use magnetic force microscopy (MFM) to characterize superconductivity
across the superconducting dome in ${\rm {BaFe}_2 \left(As_{1-x}P_x\right)_2}$,
a pnictide with a peak in the penetration depth ($\lambda_{ab}$) at optimal
doping ($\rm x_{opt}$), as shown in sample-wide measurements. Our local
measurements show a peak at $\rm x_{opt}$ and a $T_C$ vs. $\lambda_{ab}^{-2}$
dependence similar on both sides of $\rm x_{opt}$. Near the underdoped edge of
the dome $\lambda_{ab}$ increases sharply suggesting that superconductivity
competes with another phase. Indeed MFM vortex imaging shows correlated defects
parallel to twin boundaries only in underdoped samples and not for $\rm x\ge
x_{opt}$.
