Forward modelling of Phoebe’s (a − c) radii compared against observations (blue and green error bars from Table 1) for different interior models and over Phoebe’s mean density uncertainty range. The black crosses represent the result for a homogeneous interior assuming a shape development to order 1 in small rotational parameter (similar to the case used in Castillo-Rogez et al. 2012) whereas the black-circles represent the shape obtain using the Clairaut equations developed to order 3 for homogeneous interior. The blue cross represents the values deduced from Castillo-Rogez et al. (2012) and the green one from this paper.