Under state-level "distracted driving" laws, it is illegal in most of the US to use a cellphone in your hand while driving. For novice drivers, any cellphone use while driving is also illegal in most of the US (including hands-free).

So? That's an ad populum fallacy. Remember when plenty of places thought smoking cigarettes everywhere was normal?

In addition, laws often contain compromises for feasibility. I expect many jurisdictions permit hands-free conversations partly because it's difficult to prohibit them.

If you want to argue that phone-conversations while driving are safe compared to quiet driving, you should be pointing to experiments rather than popular belief.

Does what's considered normal matter for safety? Shouldnt it be based on what the science says?

Huh? I think their meaning was pretty clear, but here's an artisanally-decompressed paraphrasing:

_________

If the delivery-person is walking, the potential impact of being distracted by their phone conversation is negligible. In that case, I sympathize and respect their efforts to conduct two jobs at once.

However the situation is very different when operating a delivery vehicle, where errors have a greater impact. In that context, their multi-tasking is no longer something to respect, but instead recklessness that should be condemned.

This is especially true if it leads to the death of a pedestrian, which might be a serious crime known as manslaughter.