For the record, my XM receiver still hasn’t recognized the switch over to DST, and is reading an hour early.
I assume that the phone was periodically checking the time, as all cellphones do. The problem was what it was choosing to tell you. I can’t speak for all cellphones, but just about every computing platform keeps track of time in GMT. When there’s a need to tell you what the time is, it adds or subtracts the appropriate number to give you the time in your time zone. That was the part that hadn’t been updated.