Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is permissible for a praying person to pick the phone while praying and say subhana Allah so that the caller will know that he is praying.
The Standing Committee for Islamic Research and Fatwa states:
If a praying person is in the position that you describe and the phone starts ringing, it is permissible for him to lift the receiver, even if he has to move a little way forward or back, or to the right or left, on the condition that he keeps facing the qiblah and he says ‘Subhan Allah’ so that the person who is calling will know (that he is praying).
It was narrated that the Messenger of Allah (peace and blessings be upon him) used to pray whilst carrying his granddaughter Umamah. When he did ruku, he would put her down, and when he stood up he would pick her up again. (Al-Bukhari and Muslim)
According to a report in Muslim, this was when he was leading the people in prayer in the mosque.
Ahmad and others narrated that Aishah (may Allah be pleased with her) said: “The Messenger of Allah (peace and blessings be upon him) was praying in his house with the door closed. I came (to the door) and he walked over and opened the door for me, then he went back to his place.” She mentioned that the door was in the direction of the qiblah. (Ahmad, Abu Dawud, An-Nasa’I and At-Tirmidhi.
Al-Bukhaari and Muslim narrated that the Messenger of Allah (peace and blessings be upon him) said: “Whoever notices something alarming whilst praying, then men should say ‘Subhan Allah’ and women should clap their hands.”
Almighty Allah knows best.
Source: https://islamqa.info/en/8647