For some comparison of difficulty, there's an old game called Squares which is very similar to yours. It does a good job of ramping the difficulty up pretty fast, but it allows the game have fun short gameplay loops because of the extra gameplay mechanics (ie, you are not just moving but collecting squares too).
Have difficulty settings. Default is "easy/moderate" so that people get a sense of it. For people playing twice or as people get more experienced and want a challenge, they can choose a more difficult setting.
Have leaderboards for different difficulty settings to encourage exploration of different settings.
Tbf my experience was the opposite. But sure if I'm just terrible or if it's harder on a phone, but my first tries were sub 20s and my highest was 45 before giving up xD
This is a great use case for using an algorithmic difficulty ramp where it can really dial in that curve to solve for getting people to play longer over multiple sessions.
