Hey @Jacqui! Welcome to our community forums! How are you today?
There are two easy ways to do this:)
Once logged into MyAccount, when you go to the "Billing & Payments" tab, you can select the billing period you're interested in at the top left and then you should be able to click on "View billing details" for the phone number you're looking for to see the details of each charge associated with that number that month.
From the "Billing & Payments" tab, you can also click "Save / Print this bill (PDF)" to view the full bill with all its details in a PDF format
I hope this helps!