A feasibility is discussed of reconstructing the scattering phase function from the light field formed in a homogeneous medium by isotropic emission from a source with a wide directional pattern. The influence of errors in light field brightness measurement on the accuracy of the phase function reconstruction is evaluated. Measurement data on angular distribution of brightness at a distance of 5 km from a Lambertian source are presented. The data are used to reconstruct the scattering phase function for water of the Lake Baykal.