If you need to change a phone number connected to something you did in Phantom, the number was usually collected by a third-party provider, not Phantom directly. Where you update it depends on which service asked for it.
Phantom Cash
Phone number verification for Phantom Cash is handled by Link, Phantom’s identity verification partner.
Only US phone numbers are accepted because Phantom Cash offchain features are currently available only in the US. For more information, see What do I need to verify my identity in Phantom Cash?
To change the phone number used for Phantom Cash verification, see I want to change the phone number used for identity verification.
On-ramp providers
Services such as MoonPay, Coinbase, or Stripe may collect your phone number as part of their own identity verification process.
To update it, contact the provider directly. You can find contact links for each provider in Contact information for on-ramp providers.
Apple or Google account
If you created or use an email wallet with a Google or Apple account, your phone number is managed through that account, not Phantom.
Update your phone number in your Apple Account or Google Account settings.