This doesn't work for me. Left to my own schedule, I go to bed later and later and wake up later and later.
The thing that works for me is waking up (with an alarm) every day at the same time (6 o'clock) including week-ends.
I have a "dawn simulator" clock so most of the time I'm already awake when the alarm rings. But no matter what, when it rings I get out of bed immediately. You snooze you loose!
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.
The thing that works for me is waking up (with an alarm) every day at the same time (6 o'clock) including week-ends.
I have a "dawn simulator" clock so most of the time I'm already awake when the alarm rings. But no matter what, when it rings I get out of bed immediately. You snooze you loose!