I won't argue whether or not Phone Guy and Purple Guy are the same person but what isn't up for debate is that Phone Guy is prevalent in all three games which is a big issue in terms of continuity and plot.
Remember how I mentioned that FNAF is obviously a linear story? Well, Phone Guy dies in FNAF 1 (or fakes his death, as some theorize) yet we hear his voice in FNAF 2 and FNAF 3. Now I know that Phone Guy's voice in FNAF 3 comes from found recordings, but in FNAF 2 there is no mention of the calls being recordings. Phone Guy also makes it clear that you are at a brand new location also notes the differences between the two offices i.e, no doors.
I guess Scott couldn't get a second voice actor.
I wonder if Phone Guy is going to make one last call in Five Nights at Freddy's 4: The Last Chapter.