This is beyond silly. You could be using your phone to factcheck something that relates to the ongoing discussion. Or having a side-chat with another member, privately expressing/requesting an opinion to provide context. Or to take quick notes. Or, nowadays, you might even be using an AI to keep a running summary of what the speaker has been rambling about in the last 50 minutes, translated from 'buzzspeak' to 'human…
I agree with you, but this doesn't mean this data is useless. You could could count how many people are using their phones by speaker. "When Alice speaks 18% of the members use their phones for more than 15 minutes, but when Bob speaks the rate is 27%." could be a proxy to understand how important the parliament thinks the subject/speaker is.
I have issues with auditory processing and attention. If you deliver information to me verbally in a format where I cannot rewind/playback, have no subtitles or text to consume alongside it, and demand my full attention, I will have objectively worse reception of whatever information you're communicating. The way neurotypicals demand adherence to these, to be blunt, ceremonies of conveyance is tiresome and interferes with the goals they espouse of communication.
In fact I would go so far as to say a lot of the time, the goal is not communication at all; it is a demonstration of one's power and authority over others. If your goal is actually communication, text is better in every way. Every reader can read at a speed of their choosing, re-read parts they missed, have a speech-to-text program read it to them if they like, stop in the middle and tend to something time sensitive, what have you. A live speech allows none of this.
So yes, I probably use my phone while you're talking. I probably have my AirPods in too, because the settings where they remove background noise and just give me the person speaking are phenomenally useful. I might even be watching or having my phone transcribe what you're saying, too. And if you're going to try and chastise me for it, fine, that's your prerogative, but then I'm probably starting a job search for a place that will appreciate my skills and not demean me for not being able to perform "good worker vibes" to your arbitrary standards.