Their idea of phone service is quantity over quality of calls. It doesn't matter to them if you do all the calls correctly and solve the problems for the customer if you don't meet their arbitrary call goals. The issue for some people working there is that hardly anyone calls the last hour that you're there (8-9 PM) and yet they're expected to get the same amount of calls on average as people working in the busy morning hours.
Even if they know you'd be easily making the goal of 70 average calls if you were working an earlier hour they'll still fire you and won't budge on moving you to an earlier shift or working the email queue.