"I keep ringing people and they're not in and then they ring back when Maisie's not at her desk."
The painfully obvious question is: why doesn't T.Aldous answer his own telephone?
The painfully bewildering answer is that he says that he has to put his 'phone through to Maisie so that if anybody rings him while he's on his 'phone he won't miss their call.
So what happens is that Maisie's 'phone rings. Somebody (far too often poor old Maisie herself) then has to trot over to T.Aldous' office, peek in, try and work out whether or not he's on his 'phone, realise that he is, trot back and tell the person who would otherwise have been confronted with an engaged tone:
"Sorry, he's on the 'phone at the moment."