Phillips, now a sophomore, redshirt freshman Jordan Wade and junior Torrea Peterson — rarely used to this point — were OU's only three defensive tackles entering spring practices, forcing Ndulue and junior defensive end Rashod Favors inside to tackle.
Ndulue and Phillips were OU's starting defensive tackles in April's spring game.
The only senior who regularly contributed on last year's offensive line was tackle Lane Johnson, who was selected fourth overall in the 2013 NFL Draft. Projected starters Tyrus Thompson and Daryl Williams each have several career starts, but the depth behind them is troubling, making St. John's expected arrival all the more important.
The Sooners also signed freshman offensive tackle Christian Daimler and freshmen defensive tackles Matthew Romar and Charles Walker, all of whom are participating in summer workouts in Norman.