I'm pretty sure the cell network itself can provide time. Not sure if smartphones use it. I think older cell phones that didn't have GPS or a data plan (voice

I'm pretty sure the cell network itself can provide time. Not sure if smartphones use it. I think older cell phones that didn't have GPS or a data plan (voice only) did use it. ~15 years ago, I had an old flip phone that had an option to set the time manually or automatically, and T-Mobile "helpfully" provide a time source that was like 5 minutes slow.