"Anna is with me and she'll stay with me"

Around the 20th minute, after Mark finds out that Anna has left the apartment in the middle of the night, he gets a phone call and a male voice says this. The movie makes it clear that this is not Heinrich since he's been away and he hasn't seen Anna in a while, besides the voice sounds like Sam Neill, not Heinrich. So is that the unfinished version of the tentacle monster/Mark's doppelganger that we hear on the phone? Makes me wonder how is it able to speak in it's unfinished form, is it some kind of a demon (bullets don't hit him?) playing tricks with Mark's imagination? It's probably not important as the "monster" is used for symbolic purposes but for some reason I couldn't get this phone call scene out of my head... Curious if anyone thought anything of it.