change my phone number and can't change keychain

Are you trying to make the change in System Preferences/iCloud/Keychain/Options? What happens when you try?

Quote from the link below.

The device that is using the SMS-capable phone number you provided when you first set up iCloud Keychain. A verification code is sent via SMS to this phone number. If you can't access this number, contact Apple Support, who can verify your identity, so that you can complete setup on your new device.

Frequently asked questions about iCloud Keychain - Apple Support

Click the blue link and contact Apple support.

Go to MyAppleid.com and edit your changes then proceed. You may need to sign out of iCloud and back in on each device you have that Applied.

Dears

I want change my telephone number in icloud

Thanks

http://www.apple.com/support/icloud/contact/