In my experience yes, if you are talking to a member of the opposite sex on the phone (who is single as well) then it may be construed as dating...I heard that several times. Mind you, the elders in my hall were really anal so I'm not sure if that is unusual or not.
Sounds like this "sister" has nothing better to do than get the elders involved...doesn't she have some doors to knock on or something?
MMO