Thanks for joining this thread, @Enzo.

I recognize how convenient it is to add a customer's phone number to an invoice. At this time, the said option is unavailable. And we can't provide updates as to when this feature will be rolled out.

You may consider adding the phone number in the billing address section or entering it directly into your other sales information as a workaround.

QuickBooks developers always search for ways to improve user experience by promoting helpful and efficient features and functionalities to streamline processes that suit your business needs. By this, I recommend sending feedback so they can determine what features to be added for future enhancements.

Here’s how:

1. Go to the Gear icon at the top, then select Feedback.
2. Enter your comments or product suggestions.
3. Click Next to submit.

You can track your feedback through the QuickBooks Online Feature Requests website.

If you'd like to personalize and add specific details to your sales forms, check out this article for complete instructions: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Please don’t hesitate to reach back out if you have any other questions or concerns besides adding the customer's phone number. The Community team is always here to help. Take care!