  We propose a new generalised formalism for estimating the quantum phase
uncertainty of pure and mixed continuous-variable quantum states and compare
this with the phase uncertainty given by the quantum Fisher information. In
order to preserve the Hermiticity of the operators, we use the Heisenberg and
Schroedinger uncertainty relations to derive expressions for the phase
uncertainty from generalised Susskind-Glogower operators. This formalism not
only offers the possibility of directly measuring quantum phase uncertainties
in a cavity-QED experiment but also gives a significant computational saving
over the quantum Fisher information approach, which requires diagonalisation of
the density matrix.
