I can't think of a time I saw a cyclist checking his/her phone while cycling, I'm sure it's happened, but not too common around here. I consider myself a very focused rider, but it does take practice. I've been distracted before by focusing on what's in my mirror or looking at my computer, but I've trained myself to always have my eyes darting around.
Thing I notice is that a fair number of cyclists don't look before they change their line, I always make a wide berth when passing.
However, I live in Florida and there are a lot of hot, scantily clad females...I'm still practicing....
