Philip received his PhD in Communication Sciences from the University of Michigan under the supervision of David McNeill, following his undergraduate degree in mathematics.
He taught in the psychology and linguistics departments at the University of Washington until 1999, when he moved to the University of Missouri-Columbia, where he is professor and chair of Communication Science and Disorders.
One major focus of his research is assessment of language development, including parent report (he is a member of the team that developed the MacArthur-Bates Communicative Development Inventories), computerized analysis, and standardized testing. Other research themes are the outcomes of early language and/or cognitive delay, parent-child joint bookreading, the evaluation of intervention, cross-linguistic comparisons, and increasingly in recent years, behavioral genetic research on language development.
Currently he is a collaborator on the Twins Early Development Study, a very large, UK population-based study of early language development examining the role of genetic and environmental factors.