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 'humanspeak'. All legit uses of technology, which enhance the politician's attention rather than detract from it.
I'm not saying I'm having a hard time believing people 'could' be checking out 9gag instead during parliament, but unless you give me an AI that can detect people who are on their phone AND verified to be slagging off, then you're just bullying people for having phones and being able to use them.
Also, I like how laptops are somehow exempt from this bullying for some magical reason.