To the gymnastics expert (aka standing on his head), the first question was has IATA or some similar body issued a directive or other notice on the subject (clear now????)
On the questions orginally posed - putting aside the issues of telephone courtesy, security, etc. - is there an international directive or other notice on the subject and what discretion do the airlines have? Or why do CX allow you to use the phone until the door closes as opposed to Iberia who won't allow a phone on even walking down the corridor to the airbridge?