I got confused about the time for dawn prayer as there was a time difference between my phone clock and the calendar. So I disregarded my phone clock and I kept drinking till I heard the call to prayer. Is this valid?

The important thing is the arrival of prayer time. If the timing of your phone clock is correct, you must make up the missed fast day. If the timing of the mu`ezzin (caller to prayer) is correct, your fast is valid.