  Brown dwarfs in ultra-short period orbits around white dwarfs offer a unique
opportunity to study the properties of tidally-locked, fast rotating (1-3 hr),
and highly-irradiated atmospheres. Here, we present phase-resolved
spectrophotometry of the white dwarf-brown dwarf (WD-BD) binary SDSS 1557,
which is the fifth WD-BD binary in our six-object sample. Using the Hubble
Space Telescope Wide Field Camera 3 Near-infrared G141 instrument, the 1.1 to
1.7 $\mu$m phase curves show rotational modulations with semi-amplitudes of
10.5$\pm$0.1%. We observe a wavelength dependent amplitude, with longer
wavelengths producing larger amplitudes, while no wavelength dependent phase
shifts were identified. The phase-resolved extracted BD spectra exhibit steep
slopes and are nearly featureless. A simple radiative energy redistribution
atmospheric model recreates the hemisphere integrated brightness temperatures
at three distinct phases and finds evidence for weak redistribution efficiency.
Our model also predicts a higher inclination than previously published. We find
that SDSS 1557B, the second most irradiated BD in our sample, is likely
dominated by clouds on the night side, whereas the featureless day side
spectrum is likely dominated by H$^-$ opacity and a temperature inversion, much
like the other highly-irradiated BD EPIC2122B.
