Yes, the episode is creepy up to a point. And Jean Marsh (Doctor Who - three different roles) gives an effective one-woman performance. But the episode doesn't make any sense! She doesn't desserve to die, there's no reason given for her dying, and apparently she lives in a totally empty apartment building as no one else is bothered by the constantly-ringing phone.
Plus while the constant ringing, the pounding noises, and the holes in the wall are creepy, the whole thing is ruined when the phone "comes to life" by someone pushing it along the floor with a POV camera and some wire F/X to get it to wrap around her neck.
So... apparently this woman just had the bad luck to sublet an apartment next to a killer phone. Oh well. I remember seeing this when it was first on and remembering it didn't make much sense. I thought I'd catch it on the SciFi marathon October 2006 to see what I missed... and I hadn't missed anything. Oh well.