For me it's not even a conscious effort, as it feels rude to be on your phone, when you are having a meal with someone. Is it not rude to start reading a book while you are having a lunch with someone, why is the phone any different.
When there is a need to look at your phone (Important message, a call, or even to look up something), I think the polite thing is to excuse yourself, do the thing really quickly, and get back to your meal.
I'm sorry, I'm not a native English speaker, and sometimes I fall into these mistakes.
I think what threw you off is my incorrect punctuation, as I should've wrote it as
> Is it not rude to start reading a book while you are having a lunch with someone? Why is the phone any different?
You're right ! I kept reading it inverting the two first words. I even double-checked when posting because that seemed illogical. Funny how I somehow needed someone to point it out to be able to read it right.
It happened to me in French a couple of months ago. I read the sentence 5 to 6 times to be sure, I even quoted it in my reply, to express how illogical the proposition was.
And then the guy replied that I misunderstood. I was like: " impossible, I double-triple-quadruple-checked and quoted the relevant part". And then, blast! I saw that I got lost in the position of the negative part (it wasn't even a very complex case where negations are chained, as it happens sometimes). Worst thing is that the way I understood it, it didn't have much grammatical sense, whereas the real sentence was correct.
And the fact that I had quoted the sentence proved that he hadn't edited in between. Else I would certainly have blamed him for that: I was so sure of my cautious multiple checks...
I was ashamed of myself.
(I had troubles with "is it"/"it is" in the present case too, I had to re-read the sentence 3 times to be sure. What confuses me in English is not really the grammar, it is the abundance of very short words, they scramble the structure of the sentence, for they are less recognizable and distinguishable from each other.)
When there is a need to look at your phone (Important message, a call, or even to look up something), I think the polite thing is to excuse yourself, do the thing really quickly, and get back to your meal.