  Magnetic fluctuations in the solar wind are often observed to maintain
constant magnitude of the magnetic field in a manner consistent with
spherically-polarized large-amplitude Alfv\'en waves. We investigate the effect
of spherical polarization on the magnetic spectral index through a statistical
survey of magnetic fluctuations observed by Parker Solar Probe between
20$R_\odot$ and 200$R_\odot$. We find that deviations from spherical
polarization, i.e., changes in $|\mathbf{B}|$ (compressive fluctuations) and
one-dimensional discontinuities, have a dramatic effect on the scaling behavior
of the turbulent fluctuations. We show that shallow $k^{-3/2}$ spectra are only
observed for constant magnetic field strength, three-dimensional structures,
which we identify as large amplitude Alfv\'en waves. The presence of
compressive fluctuations coincides with a steepening of the spectrum up to
$k^{-5/3}$. Steeper power law scalings approaching $k^{-2}$ are observed when
the fluctuations are dominated by discontinuities. Near-sun fluctuations are
found to be the most spherically polarized, suggesting that this spherical
state is fundamental to the generation of the solar wind. With increasing
distance from the Sun, fluctuations are found to become less three dimensional
and more compressive, which may indicate the breakdown of the Alfv\'enic
equilibrium state.
