Hey there MayaCwl,

Thanks for reaching out to us here. QuickBooks Online is a great tool able to help keep your books balanced. I would be happy to provide some information.

The customer phone number doesn't flow into the sales transactions (estimates, invoices, sales receipts). However as a workaround, follow these steps;

1. Click on customers on the left.
2. Click on customer name and edit their information.
3. You can add customer phone under the Billing Address or use the Country field.
4. Save.

If you have any other questions, feel free to reach back out to us here.