Hi there.
I'm in exactly the same boat - my mother lives in the UK and I live in the US. While I don't have the problem with the TV (as mummy can no longer remember how to turn it on, let alone turn it off) I have had many occasions where the phone has been put down and then can't be found again. I can hear a little voice from somewhere in the room saying "Jenny? Jenny?" and there's me screaming down the phone "PICK UP THE PHONE! THE PHONES HERE!!" I have learnt NOT to ask any questions that might require her to look for something. Our telephone conversation is now extremely limited - apart from anything else she spends a great deal of her time asleep, and I'm not particularly lucid when I wake up, so I can't expect her to be. If I want to have anything more than a basic "just checking you're still alive" call, I call her carer, and get her to place the call when she goes in and mummy is awake and aware.
As for conversational topics, I am stumped. Like your mother, mine can not for the most part remember if she's eaten or whether she's been anywhere. Actually her world has closed in on itself - she rarely asks how her beloved grandchildren are. Topics I have learned to avoid: Pets and gardening, because because both result in sadness on her part. In the past I called her regularly, and we discussed evertyhting under the sun, but not any more.
Not much help. I'm afraid, but you're not alone. The only suggestion that I have found to be any use at all, is to make sure that you call only when there is someone else there.
Jennifer