A method to obtain the Duvall phase function from the structure of a stellar model is presented. This can be a good tool for understanding the dependence of p-mode frequencies on the structure of the upper layers of the convection zone. A linear relation between phase function differences of two models and their equilibrium structure differences is obtained. The validity of this expression was tested against solar models. These models are also useful for estimating what kind of information can be obtained from observational Duvall phase function determinations.