How to get custom number format to save as text

Hi, I'm having some trouble with storing phone numbers. I have a bunch of phone numbers I am keeping a record of, with the purpose of uploading them, formatted, to another site. I have used a custom number format to change this:

1234567890

Into this:

+1 (123) 456-7890

While this looks good in Excel, it does not transfer to the site very well. I figured out that to transfer properly, the phone number must be stored as text (and not a custom number format). Is there any way to capture the "+1 (123) 456-7890" part of it and turn it into text? I have over 4,000 phone numbers, so writing the format out by hand is not possible.

Thank you!

Just thinking out loud here (might be a much more obvious answer), but could you add your Custom Number format into a TEXT function and use that as a new field to upload? If that also doesn't work, you could join a null value to those results and create a third new field to try to upload.

Thank you both! The TEXT option worked.