The quantum properties of the two-dimensional relativistic spherical membrane in phase space are analyzed using the Wigner function. Specifically, the true vacuum and rigid bubble nucleation cases are treated. Inspired by quantum cosmology, the Hartle–Hawking, Linde and Vilenkin boundary conditions are employed to calculate the bubble wave functions and their corresponding Wigner functions. Furthermore, the asymptotic behavior of the wave function using three different methods is explored and the Wigner functions are calculated numerically. Some aspects of the semiclassical properties for each boundary condition and their possible implications for quantum cosmology are discussed.