Presbyterian's Armel TeTe made a layup to open the scoring in overtime but the Blue Hose (11-18, 4-12) went 0 for 6 from the field, missed their only free-throw attempt from there and Radford closed on an 8-0 run.
Davon Bell hit a 3-pointer to give Presbyterian a 66-65 lead with 13 seconds left in regulation but Phillips hit 1-of-2 free throws with a second left to force overtime.
Senior Ruben Arroyo, who came in averaging 3.4 points per game, hit five 3-pointers and finished with 17 points -- both career highs -- for the Blue Hose. Bell added 16 points and six assists.
Bruce Pearl has Auburn back in the Sweet 16
The Tigers dominated Kansas on Saturday for their 10th consecutive win and the coach's first trip to the Sweet 16 in nine years.
Auburn blows past Kansas 89-75 to reach Sweet 16
Bruce Pearl's Auburn rebuilding project took a massive leap.
Edwards sets Purdue record in 42-point performance
Carsen Edwards hits nine 3-pointers, a Purdue record, and scores a career-high 42 points in the 87-61 win over Villanova.