  The detection of high energy neutrinos ($10^{15}-10^{20}$ eV or $1-10^{5}$
PeV) is an important step toward understanding the most energetic cosmic
accelerators and would enable tests of fundamental physics at energy scales
that cannot easily be achieved on Earth. In this energy range, there are two
expected populations of neutrinos: the astrophysical flux observed with IceCube
at lower energies ($\sim1$ PeV) and the predicted cosmogenic flux at higher
energies ($\sim10^{18}$ eV). Radio detector arrays such as RICE, ANITA, ARA,
and ARIANNA exploit the Askaryan effect and the radio transparency of glacial
ice, which together enable enormous volumes of ice to be monitored with sparse
instrumentation. We describe here the design for a phased radio array that
would lower the energy threshold of radio techniques to the PeV scale, allowing
measurement of the astrophysical flux observed with IceCube over an extended
energy range. Meaningful energy overlap with optical Cherenkov telescopes could
be used for energy calibration. The phased radio array design would also
provide more efficient coverage of the large effective volume required to
discover cosmogenic neutrinos.
