Based on meta-analysis, a strong link between social anxiety and phone use has been established in the literature, but the underlying mechanisms of why social anxiety might cause people to use their phones are poorly understood. Intolerance of uncertainty is a transdiagnostic factor of many anxiety disorders and may help explain why socially anxious people tend to use their mobile phones as a tool to cope with, or distract from, inherently ambiguous social interactions. This non-experimental, correlational study had four core aims: to examine whether increases in social anxiety would relate to 1) increased phone usage during social interactions in groups, or 2) phone dependency; to examine whether intolerance of uncertainty and motivation to use phones mediates either of these relationships. To test these models, an opportunity sample of 252 participants completed a series of online questionnaires containing measures of social anxiety, intolerance of uncertainty, and phone usage. Correlational analysis of results showed increased phone dependency and phone use in social groups for people with high social anxiety. Serial mediation analysis showed that people who were more socially anxious also reported higher levels of intolerance of uncertainty, greater motives to use phones to reduce anxiety and higher phone use. We discuss these results with specific reference to compensatory internet use theory. In sum, it appears that for people with social anxiety, phone use in social situations tends to be motivated by reducing anxiety.