That is bizzare
The ringing phone could not have been an incoming call, as there would be no mobile phone signal at cruise altitude, and even if there was, whoever was calling would eventually give up.
More likely to have been an "alarm" that had been set, but I would have thought that after 3 or so automatic 'snooze' resets, the phone itself would have given up.
Most plausible explanation, however..............a kids toy phone!
