In this report we are interested in the collective motion evolution of self-propelled synthetic particles in a microfluidic circular chamber. We have worked with an experimental model that motorizes colloids of 5 and 10 micrometers and we have studied the flocking dynamics according to the variation of the density injected in the chamber, which is taken as the control parameter of the system. The colloids experience a transition between a low-density and a high-density phase, in which the interactions of particles velocities leads to the emergence of collective motion and the formation of a vortex inside the circular chamber. We were able to show the phase diagram of the transition correspondent to this system from the experimental results obtained.