a note feels like it would be better for your friend
My advice: think about whether you want to do this for you or for your friend
If its for you, and you want to be able to talk to your friend in that moment, that's completely valid.
However, if you're thinking about your friend, there are many reasons why a note would be better. For example, if theyre on the phone, they will inevitably feel like they had some part in it happening, even if you tell then otherwise. A note would also give them more agency in when/how to deal with the situation, rather than forcing them into something.
Hope that helps and hope you find peace