It is a US phone number?

yes

https://ttlc.intuit.com/replies/7416798

I've already done everything you said to do, even checked my Account Records which has the same phone number I'm trying to put it.  It continues to tell me Invalid Phone Number.

Can you attach a screenshot so I can understand exactly what screen you are on?
Please REMOVE any personal information before attaching a screenshot.

Never Mind. I've closed my turbo tax records and filed my extension via IRS Website.