By Rabbi Yosef Ginzburg.
Translated for COLlive.com from Sichat Hashavua
When the cellphone rings in the middle of davening it disturbs not only to the owner of the device, but has a double problem to it:
Bein Adam Lamakom (between man and Hashem) – At conventions and meetings we silence our phone, but when standing before Hashem we leave it on?
Bein Adam Lachavero (between man and his friend) – When a phone rings it disturbs the entire congregation.
Therefore it is an obligation for one to turn off his mobile before walking into Shul (or at least switching it to vibrate).
Clearly it is forbidden to answer a call in the middle of davening. (A person dealing with life-threatening situations – Pikuach Nefesh – like a physician or Hatzalah member, should daven near an exit door so he can take the call outside).
One who is daveing Shmona Esre is forbidden to move from his place until the end and should stand in front of Hashem as a servant before a master – with awe and fear.
He is not allowed to occupy his hands with anything – even the most simplest of movements, and especially not signal with his fingers to someone or something. That includes a syllable of rebuke, encouragement or anger.
But it is says in halacha that if a baby cries in middle of Shmone Esre and disturbs the minyan, his father should stop devening and try to sooth him without speaking. If it does not help – he should take the child to another room.
Therefore, if the phone rings his owner should stop the ringing immediately, even if he is in middle of Shmone Esre. (The same is if he is davening alone in his home and the phone disturbs him).
If a sefer (book) falls on the floor and is disturbing him from davening Shmone Esre, and especially Tefillin or their case; or if a window is open and the wind disturbs him – one is allowed to move and even away from his current location (and return to his place and continue davening).
(Sources: Brachos 30,2; Shulchan Aruch Orach Chaim 104, 61; Shulchan Aruch Admur Hazaken 61, Mishna Berura 160, 1; Piskei Teshovos 100, 1 & 3)