The significance of this will vary, largely based upon the range of the car. Think about how many cycles the battery takes after 100,000 miles on a car with a 100 mile range vs one with a 300 mile range, for example.
In addition, car batteries have:
a) vastly better charge controllers than the cheap crap that's put in phones
b) better quality cells to start with, or at the very least higher QA standards
c) BETTER CHARGERS. Cheap cellphone chargers can kill the battery with their unclean power, especially when linked with cheap charge controllers in the phone.
d) better thermal management with cooling and (iirc) heating, compared with a cellphone battery that has to endure anything between double-degree negative temps in winter to +40 °C when it gets held by the user or the CPU gets active.