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In my view it is the same as a car user being annoyed at a cyclist in primary position.
The two aren't really equivalent, there are good reasons to cycle in primary related to your safety as a cyclist (controlling the overtaking, avoiding being squeezed, etc).
I struggle to think of reasons why cycling whilst looking at your phone would be safer but it's pretty easy to make the arguments why it is less safe.
Lights not on is illegal. Phone isn't.
Why not politely say something, like "You are weaving across the lane and endangering me by cutting me up with no warning and little space. Maybe it is because you are using your phone?"
If you can form the phrase with an actual, objective, danger at the front then it would probably be worth saying. Otherwise it's just your opinion on how someone else should conduct themselves. In my view it is the same as a car user being annoyed at a cyclist in primary position.