The first calculation phase (Initial phase) in the 3D FOUNDATION program is always a calculation of the initial stress field for the initial geometry configuration by means of gravity loading.
In contrast to other PLAXIS products, the 3D FOUNDATION program does not contain a quick procedure to generate the initial stress field on the basis of soil weight and K0-input (known as K0-procedure). Therefore, the initial phase represents a real finite element calculation in which soil weight is applied by means of gravity loading. If not all geometry components are active in the initial situation, the user must deactivate these components in the draw area .
After this initial phase, subsequent calculation phases may be defined by the user.
Reference:  PLAXIS 3D FOUNDATION Reference Manual version 1.