Is it permissible to rely on the timings written in the schedules used in Europe for the times of Adhan, Imsak, and Iftar? Is it permissible to drink when the Adhan for Fajr begins? Must that day be made up?

A fasting person must abstain from the second dawn until sunset. The decisive factor for its arrival is knowledge, whether through a correct adhan or a correct calendar. If the adhan or the calendar is correct, then one must abstain from their beginning. If a person doubts the entry of the dawn time, they may eat and drink, and there is no make-up required if their doubt persists.

Based on this, make-up is required if the calendar was correct and the phone's clock showed a correct time. However, if one is ignorant of which is more accurate and doubts the entry of the time, then no make-up is required. Some scholars permit eating or drinking for a minute or so if the muezzin relies on the calendar.