  We study squeezing properties of the fluorescence radiation emitted by a
driven $\Lambda$-type atom in which the metastable lower energy levels are
coupled by an additional field. We find that the relative phase of the applied
fields can significantly modify the squeezing characteristics of radiation. It
is shown that the additional field connecting the lower levels in the system
can induce spectral squeezing in a parameter regime for which the squeezing is
absent without the additional field. Moreover, the squeezing can be shifted
from inner- to outer-sidebands of the spectrum by simply changing the relative
phase. A dressed-state description is presented to explain these numerical
results. The phase control of squeezing in the total variance of quadrature
components is also examined. We show that the squeezing in total variance
attains its maximal value when the system reduces to an effective two-level
system.
