What if you prepare what you want to say ahead of time (on paper in case you forget things under pressure, like me ... and then call your boss when you are ready? Like set a time of day like Thursday at 10:30am and just make the call. This way you don't have to fear the phone ringing because YOU are in control of the time of the call.

Ask for what you need in a direct but kind way. Explain as much as you want or as little as you want, but identify how much you are willing to share in advance so you don't feel pressured to reveal more than you want to. Prepare some possible phrases that could be used to redirect the conversation in case your boss is asking things you are not comfortable with.

I hope you get the time off that you need.