It's all stored on Strava. You just push a button when you start running and when you stop. If it's habit, you notice pretty fast if you don't have your phone, especially if you listen to music or something when you run.

I don't run as much, and never more than 1h, yet it happened several times to me that my phone battery died on me while running. (I'm obviously not carrying a powerbank with me, and my phone is many years old). It would also expect that Strava or the network would fail from time to time (no need to go as far as antarctica for that - I've been living in germany for less than a year and I have lost track already of how many times the 5G/4G network has been out of order for hours). I guess strava has a good networkless mode. Or maybe my experience with tech has been particularly bad and I'm an outlier?