DePhillips earned a bachelor's degree in government from Georgetown University in 1987 and a law degree from Seton Hall University law school in 1992.

He served on the Wyckoff Township Committee from 2010 to 2013, serving as deputy mayor in 2011 and mayor in 2012. DePhillips was a Northwest Bergen County Utilities Authority commissioner from 2012 through 2017, and chaired the 40th District Republican County Committee from 2014 to 2019.

In April 2024, DePhillips became a partner at the law firm of Bernstein DePhillips & Kalosieh in Bergen County. He previously served as general counsel and chief operating officer at Porzio Life Sciences, an RLDatrix Company that assists pharmaceutical, medical device and biotechnology companies with regulatory and compliance challenges related to sales, marketing and strategic business operations.

He and his wife, Patti, reside in Wyckoff with their four children.