I can't remember the phone number to login to my iCloud

Hello raaaaaaa4,

Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with changing your phone number to log into iCloud. If you're referring to the phone number you use for two-factor authentication, this article shows how to manage your trusted phone numbers: Manage two-factor authentication for your Apple ID from iPhone - Apple Support

"Add or remove a trusted phone number

When you enrolled in two-factor authentication, you had to verify one trusted phone number. You should also consider adding other phone numbers you can access, such as a home phone, or a number used by a family member or close friend.

1. Go to Settings  > [your name] > Password & Security.
2. Tap Edit (above the list of trusted phone numbers), then do one of the following:

• Add a number: Tap Add a Trusted Phone Number.
• Remove a number: Tap  next to the phone number.

Trusted phone numbers don’t automatically receive verification codes. If you can’t access any trusted devices when setting up a new device for two-factor authentication, tap “Didn’t get a verification code?” on the new device, then choose one of your trusted phone numbers to receive the verification code."

If you're referring to the phone number to change your password, unless you can access your Apple ID you would be unable to change it. We would recommend proceeding with account recovery as described in the article at the top of the page.

We hope this helps.

Cheers!