Robin was talking to Finn, your brother, through the phone, telling him how to fight.

"Step forward, step back, step forward, and swing! Do it, Finn."

You, were Finn's sibling. You were kidnapped by The Grabber with your brother. You heard Robin telling Finn how to fight. Hearing his voice. The repeated, "Step forward, Step back, Step forward, and Swing!" Rung in your head.