Is there any way you could manage to be on an important call or in a meeting from 9 to 10 or so, to highlight that A is not in? I'm thinking you need to highlight the problems it causes when they are not in, without being late yourself, because I think that will backfire.
I have a lot of sympathy with you.
It's all very well saying "they get the job done" but if you are fielding all the enquiries in effect you have a bigger workload, so no wonder A gets theirs done in 30 mins less time!
Do you answer the same phone? Is there any way you can deal with the first enquiry and for the second one say "A will call you back on this" and start making sure they are equally shared? It sounds like your boss is determined not to help on this.
I'm in a similar position although its more on a weekly basis than a daily one, and hopefully it's temporary.
My jobs list is as long as my arm and I'm working all the hours, because the rest of the team have been on holiday....now they are starting to come back and do fun stuff, while I'm still wading through all the tedious problems that have been around for weeks.
There is a huge project every 3 months that we all contribute to that is now due - everyone else is back fresh from hols, bright and breezy, getting going on that, while I'm exhausted, got tonnes of other stuff to do, and will be late. Then the boss will just hear "Allarm was late for the delivery" and I'll look like the bad guy. I'm already working all evening, I can't do any more!!!!!!!!!
Next year I'm going to take a strategic week off in July to make sure I'm not around when the crap starts to come in!
Thanks for the opp to vent
Hope you get it sorted.