So this Nanny works Monday, Wednesday and Friday for you between the hours of 9am - 3pm...
First, I have to say, I am absolutely amazed that she's had the disrespect to TELL YOU that she wants a break of 15 minutes per hour! Wowsers; I have never been in a job where I've had that privilege😂. That would mean she's working only 75% of the time you employ her and she's finishing at 3pm!
She has ample opportunity to phone people when she's not working, or after 3pm. Certainly, when I was working as a teacher it was very strict policy to never use your phone in lesson time, and to have it on silent. Personally, I enjoyed being away from all the stuff going on at home, and yes, I would phone post lessons. Many people assume teachers 'only' work until three, but in actual fact I'd generally finish at 6-7pm. Weekends meant one entire day marking. But yes, it was the job I chose to do because I love working with challenging teenagers.
I think in all situations where you take on a nanny, a new class, whatever; YOU STIPULATE in writing what your expectations and boundaries are. Make them as clear as can be.
Working those sort of hours, I'd definitely expect her to use her phone in her break. I mean, she can phone back whoever, without neglecting her duties. Have you asked her what she's doing on her phone, Clips?
I'd be inclined to sack the nanny, TBH, finding solid grounds to do so. Then I'd start afresh, but this time I'd have it written in black and white, literally what you expect of her. Her breaktimes are ridiculous, for starters! But you also need to think about any other duties you expect, such as cleaning, cooking, tidying up, input with your children, etc. That way, you wouldn't be having to have so many breaks yourself.
There is a word that comes to mind here that you need to enforce; ASSERTIVENESS.
YABU by not enforcing your wishes.
I'd come and work for you if I had breaks every hour of 15 minutes, worked three days a week, didn't have a mountain of work to take home and worked three days a week. Plus, all my so called 'holidays' that people think I get are used up, lesson planning, making lessons interesting, interactive and engaging. I get so peed off with people assuming that because I'm not at work on my summer break, etc, when I'm actually working at home. I've even had the odd cheeky parent tell me to look after their children "because I'm being paid, but not actually working, so therefore I should look after their children!". Wtf! They get short, sharp shift from me and a big fat "No". No apologies!
I would be expecting your nanny to be a hell of a lot more interactive with your child, by doing some painting, going for a walk, playing games, etc. Now if she were to show you some nice photos of what/where they've been, I'd be ok with that.
This nanny is basically taking the piss!
I'll come and work for you; yes, I can hear all the nannies shouting out saying it's hard work, but TBH, after dealing with back to back lessons of 30+ teenagers every lesson, with a non existent break of fifteen minutes after an hour(dealing with teenagers, then 35 minutes for lunch, finishing at 6-7pm, relatively, it'll be a doddle☺️💤.