Keep the king out, then check from behind.
In the Philidor defense, the defending king blocks the pawn’s advance and the rook holds the third rank from the defender’s side. Once the pawn advances to that rank, switch to checks from behind. This method applies to the right rook-and-pawn position, not every ending a pawn down.
Check where the king must move
Your rook gives check. No legal move captures the checking piece or blocks the check, so the king must move.
2 more clean runs (at any point) to reach Recall.