In an attempt to reduce the negative consequences of adolescent media use, parents often monitor their children's online activities. However, research suggests that parental monitoring often does not reduce children's problematic mobile phone use as expected. Based on the results of a survey of 584 Chinese adolescents, we found that parental monitoring positively predicted children's problematic mobile phone use (PMPU) within a Chinese cultural context. The results also showed that children's escape motivation partially mediated this relationship, while their level of shyness moderated both the mediated path and the direct impact of parental monitoring on children's PMPU. The findings suggested that a higher level of shyness increased the likelihood that parental monitoring would increase the child's escape motivation and PMPU. The study results provide guidelines for parents and educators regarding interventions for adolescents' problematic phone use.