Placing the phone: stand it upright in front of you or to your side, 2–3 metres away and low down, so your whole body is visible standing and in sajda. A side view is the most reliable.
Tap the small camera in the corner to enlarge it while placing the phone, then tap again to shrink it. How it counts: one rak'ah = two sajdas, with sitting up between them. The number goes up only after the
second sajda. Use +1 / −1 if it ever miscounts.