I think the key point from OP was paying closer attention the when they went to sleep.

If you know you have to be up by X then be sure to go to bed at X-Y. I would imagine the struggle is winding down for bed early rather than waiting till you "feel tired" to go to sleep. Artificial light and stimulation makes it easy to stay up way later than intended.

For me, it's easier to wake early than sleep early. Whatever I want to do after midnight, I can do before dawn. And that plays into the artificial light thing of waking me up.

Once you're tired from waking early, you're far less likely to look at your phone too late.

Luckily I went through a similar experience in college, so when I got rid of the alarm I slowly but surely looped around a bit, until I got the napping right.

However - then I started a job where I had to travel between time zones, and I still haven't figured out how to get the body to know that it's traveled quickly other than mealtime & nap manipulation the day before, and even then I still need alarms.

You likely have DSPS, worth taking a look at: https://supermemo.guru/wiki/Curing_DSPS_and_insomnia which has many helpful suggestions (that could work better than alarm clock)