In all likelihood another payphone. All sorts of businesses had them in the 1980's for customer and staff private use.
No, it doesn't say it was a payphone, it gives an address, unlike the others...
In any event there were many other logged calls in the metered call logs on other dates, which were of different duration and which were made at different times of the day, which enabled the police to trace calls which had been made from whf between 6pm on Tuesday, 6th August 1985, and 8am, Wednesday, 7th August 1985. It was possible for the police to trace certain calls which are detailed in these metered call logs, because some were identified easily. For example, the call made by June Bamber to her sister Pamela at 10pm on evening of Tuesday, 6th August 1985. Another call identified which was made from the scene to the police at 3:26am, followed by the activation of the attack alarm at about 3:33am. Somewhere sandwiched in between the call made by June to her sister Pamela, and the call made to the police from the scene at 3:26am, was another much shorter call which satisfied the police that a call had been made to Jeremy's cottage from whf that night...