In 1993 he was appointed Danforth Professor of Philosophy of Religion at the Claremont Graduate University in California, and thereafter divided his time between Claremont and Swansea where, in 1996, he became the Rush Rhees Professor Emeritus and Director of the Rush Rhees Archives and Peter Winch Archives based in Swansea University.

Phillips gave many endowed lectures during his tenure at California's Claremont Graduate University.

His teachers at Swansea – J. R. Jones, R. F. Holland, Peter Winch, and, most importantly, Rush Rhees inspired a devotion to philosophy.

On this view, philosophy is an activity involving both inquiries about reality and elucidations of the various contexts in which people live and speak.

In contrast to the New Wittgenstein school of thought, philosophy is not limited to purely "therapeutic" treatments and the removing of philosophical confusion.

He was instrumental in the founding of the Taliesin Arts Centre on the university campus in Swansea, and promoted the use of the Welsh language in local schools.