The causes and results of inhomogeneous phase on oscillatory magnetization are considered and methods for determining experimentally whether phase inhomogeneity is producing significant deviations from the Lifshitz‐Kosevich theory are discussed. General expressions are derived for (i) the reduction in oscillation amplitude and (ii) the relative phase shifts between harmonics which result from inhomogeneous phase. For the specific case of a parabolic field distribution, several universal curves are given for estimating the size of field inhomogeneity effects as a function of the magnetic field strength and of the sample position along the field axis. The effects on the measured values of the collision parameter and absolute amplitude are also considered and these effects are illustrated by experimental results from oscillatory magnetization and magnetostriction measurements.