Customer service representatives (CSRs) as organizational boundary spanners inevitably experience role stress due to conflicts demands or ambiguous job expectations. Prior studies reveal inconsistent findings regarding the relationship between role stress and CSRs’ job performance. To address this issue, we differentiate role conflicts into supervisor-related and customer-related and investigate their respective effects on job performance, through adaptive service behaviors (ASB). Moreover, we postulate that role ambiguity congruent with the source of role conflict could mitigate the negative effect of role conflict on job behavior. This study tests with 229 CSRs working in a call center. The results show that supervisor-related and customer-related role conflict both negatively relate to CSRs’ ASB which positively relates with job performance. The findings also indicate that the negative effects of supervisor-related role conflict on ASB is weakened when CSRs perceive high role ambiguity regarding supervisor’s expectation, whereas the negative relationship between customer-related role conflicts with ASB decreases when employees experience ambiguous requirements on operation. This study suggests that stressor, i.e., role conflicts might increase the degree of CSRs’ ASB, depending on degree of constraints on their role expectation that is related to the source of conflicts, which has significant implications for managing frontline service employees.