The Phillies selected Nelson's contract from Triple-A Lehigh Valley on Wednesday, Todd Zolecki of MLB.com reports.
Nelson was outrighted off the 40-man roster last month but earned his way back on by allowing just one run over his last 9.1 innings at Lehigh Valley. He will give the Phillies a fresh relief arm after the bullpen had to cover 8.1 innings in Tuesday's win over the Blue Jays.