  We introduce a generalized version of phase retrieval called multiplexed
phase retrieval. We want to recover the phase of amplitude-only measurements
from linear combinations of them. This corresponds to the case in which
multiple incoherent sources are sampled jointly, and one would like to recover
their individual contributions. We show that a recent spectral method developed
for phase retrieval can be generalized to this setting, and that its
performance follows a phase transition behavior. We apply this new technique to
light focusing at depth in a complex medium. Experimentally, although we only
have access to the sum of the intensities on multiple targets, we are able to
separately focus on each ones, thus opening potential applications in deep
fluorescence imaging and light delivery
