Does the obligatory prayer become nullified if one invokes blessings upon the Prophet automatically or out of forgetfulness during it, especially if prompted by a constantly running phone application?

If a worshiper forgets to silence his phone and a ringtone of Salawat on the Prophet (peace be upon him) plays, the Shafi'is hold that it is recommended to send blessings upon him when his name is heard during prayer, based on the Prophet's (peace be upon him) saying: "The miser is he before whom I am mentioned, and he does not send blessings upon me." This is supported by narrations from the Salaf. The Malikis permit this quietly, without excess, while the Hanbalis, in one narration, consider the prayer of one who performs a permissible remembrance in an inappropriate place to be valid. As for the Hanafis, they believe that sending blessings upon the Prophet (peace be upon him) invalidates the prayer if it is a response to hearing his name mentioned, but not if it is initiated voluntarily. The worshiper should promptly silence or turn off the mobile phone, even if already in prayer.