NCOA phone appends question

We're doing an NCOA update with phone appends from a different vendor and we're currently on v12.5.1. We're trying to determine what the 'D' and 'F' under phone updated actually refers to. The documentation does not clarify what the difference is and the only post I've found on the forums form someone who posted this same question was from 6 years ago and they did not receive an answer. 

We're assuming that one means only part of the new number is different from the current number and the other means the entire phone number is new. Does anyone know which scenario is 'D' and which is 'F'? Thank you to advance to anyone for your help!!