Minimizing the exit route’s position in the hierarchy is incredibly likely to increase the frequency of disingenuous ratings. People might tap some random number of stars just to get out (this already happens). The very fact that people are constantly asked for some feedback causes them to sometimes pick 1 star (they are not rating the call quality but rather the quality of their call experience—which was negatively altered by the feedback ask). If you take away a perceived exit route, a higher percentage of users will feel as if they are required (rather than asked) to submit feedback (even though that’s not true).

The best flow is probably one that puts the quantitative rating behind a choice of whether or not to rate. On their first call, users should be asked to set a persistent preference of whether or not they would like to provide feedback on calls. If so, then the current flow should suffice (you still need the not now option for users to feel secure in their agency). If not, then the feedback option should be sequestered in a submenu somewhere so that they still have that option the day they have low-quality call and feel the need to tell someone.