On phones, the furigana becomes tiny if you zoom out. On a 6" screen, you will pinch-zoom constantly. Best on a 10" tablet or printed.
You can already read simple graded readers online (e.g., Tadoku.org free books). Level 0 is genuinely easy – too easy for anyone who has studied for 2+ months. Japanese Graded Readers Level 0 - Vol. 1 Pdf
Kanji appear immediately (e.g., 私, 猫, 赤い) but with furigana above every single character . This trains you to recognize kanji shapes without forcing memorization. On phones, the furigana becomes tiny if you zoom out