How to change current trusted phone number on Apple Account?

I see you are asking this about an iPhone. ;-)

The below is based on the section "About trusted phone numbers and trusted devices" in the article Two-factor authentication for Apple Account - Apple Support

To see, add, or change your trusted phone numbers use one of these methods:

● On your iPhone, iPad, or iPod touch: Go to Settings > your name > Sign-In & Security. Tap Two-Factor Authentication, tap Edit (above the list of trusted phone numbers), then enter your device passcode when prompted. Add or remove the number, then tap Done.

Similar information for the iPhone can be found here --> Use two-factor authentication for your Apple Account on iPhone - Apple Support

If you are asking how to do this because you cannot currently sign into your account, read How to use account recovery when you can’t reset your Apple Account password - Apple Support

Here is how to: Add or remove trusted phone numbers on Mac - Apple Support

And: How to use account recovery when you can’t reset your Apple Account password - Apple Support