Parental phubbing, a growing phenomenon in the digital era, has raised concerns about its impact on young children’s development. However, little is known about how parental phubbing influences preschool children’s social–emotional competence and the underlying family mechanisms. Drawing on social learning theory, attachment theory, and family systems theory, this study examines the mediating roles of family intimacy and parent–child attachment. A total of 1,113 parents of preschool children in China participated in this study. The results showed that parental phubbing was negatively associated with children’s social–emotional competence. First, family intimacy mediated the relationship between parental phubbing and children’s social–emotional competence. Second, parent–child attachment also served as a mediator. More importantly, a significant serial mediation pathway was identified, whereby parental phubbing reduced family intimacy, which in turn weakened parent–child attachment and ultimately impaired children’s social–emotional competence. These findings highlight the importance of family processes in understanding the negative effects of parental phubbing and provide practical implications for promoting young children’s social–emotional development.