Does the IRS require a phone number to file taxes?

Form 1040 Instructions indicate that phone number is optional:

Phone Number and Email Address
You have the option of entering your phone number and email address in the spaces provided. There will be no effect on the processing of your return if you choose not to enter this information. Note that the IRS initiates most contacts through regular mail delivered by the United States Postal Service.

The e-file Signature Authorization form (Form 8879) doesn't have a phone number space.

I'm not seeing anything that indicates the IRS requires a phone number to file taxes, it's not true that they never call, just that they do not typically call. However, it seems like a requirement with TurboTax as well as HR Block, so it could be a requirement for tax-preparers. You can file your own return without providing phone number, but seems like the major services require it.