Philip ended the first grand tour of the year in 43rd place, 1hr.47min 49sec behind the winner, Colombia's Nairo Quintana.
The Team Sky rider achieved one of his best career performances when he was placed third on a tough mountain leg on Thursday.
The result was Ireland's best on the Giro since Stephen Roche was third on an Italian stage in 1989.
Philip's strong performance occurred despite the fatigue of being in Wednesday's breakaway.
Cycling pundits suggested the display during stage 18 confirmed that Deignan is back to something close to his top form.
He is still building his condition after breaking his collarbone earlier this year.