Did you hire her through an agency? If so, it might be worth having a conversation with them - they usually touch base a few times toward the beginning.
Our house is a similar size and I've had a similar setup. Interestingly, when my housekeeper moved further away, we went from 5 days 40 hours to 25 hours over 3 days and she still seems to get the same amount done, so I think the PP's who said it's more hours than are necessary might be right.
We have certain things we do ourselves - I do the laundry, although might sometimes ask her to do a load, my DH changes our sheets but she does the kids'. We leave the kitchen pretty clean but not spotless at night and sometimes unload the dishwasher in the morning but not always.
I don't have her do any shopping, cooking, meal prep or childcare. She cleans, changes the kids' beds, picks up any debris, and irons (including all the sheets). She also runs the house when we're not around - i.e. deals with deliveries and collections, any builders or workmen, and waters plants. She knew the job when she took it and while she might have been used to supervising cleaning in other previous positions, she knew she would be the only staff and that it would be hands on in this one.
Truthfully, I think there's a learning curve of someone figuring out what's important to you and you figuring out what's in her line of vision - the dust is probably a bit of blind spot for some reason. Mine's been with us for years and I still have to periodically point out places she habitually misses. And, yes, she's always on that bloody phone and I agree, it not only slows things down but is distracting from the job. I remind myself that it's a job without a huge amount of intellectual stimulation and try not to begrudge it. Just today, though, I was in the office trying to get a project out and the rest of the house was quiet, so I could hear her talking endlessly for hours and sort of wanted to shoot one or both of us.
In your shoes, I would spend a day or two trying to understand how she allocates her time and if there's anything you can see that could be tweaked to make things more efficient. Ask her if she prefers if you make her a schedule or checklist - I once had someone I'd hired from an agency quit after two days saying she couldn't work for me because I wasn't structured enough.
Good luck, OP. It might be a first world problem, but it's someone else in your house, you're paying them fairly, and you have a right to expect they'll do their job well.