Abstract: Gouy phase shift of q-Gaussian laser beams interacting nonlinearly with collisional plasmas with axially increasing density has been investigated theoretically. The Gouy phase shift also known as phase anomaly occurs at a fundamental level from position momentum uncertainty. Due to intensity gradient over the cross section of the laser beam redistribution of the carriers occurs on account of collisional heating of the plasma. The resulting index of refraction resembles to that of graded index fibers that stimulates the laser beam to get self-focused. The reduction in transverse dimensions of the laser beam in turn leads to spread in transverse momentum of its photons. This transverse momentum spread then modifies the axial phase of the laser beam. Following variational theory, a set of coupled differential equations for the evolution of beam width and axial phase of the laser beam has been obtained. The equations so obtained have been solved numerically so see the effect of laser and plasma parameters on the evolution of beam envelope.