I remember when i was sitting shiva for my mother a”h and someone pulled out their cellphone i just thought it was the tackiest thing you could do at such an occasion.
I dont know the specifics and I dont know you or the person, but it could very well be the person was expecting some important information. Sometimes I tell people that I am somewhere important and dont call me, but send me a text so as not to interfere and if the text is important then I will call otherwise I can ignore