It is very essential to update your registered mobile number in Gmail because in case you forget your account password, it will help you to reset it and recover the account details. To change/update your already registered mobile number the simple steps can be followed.
Just have a glance at this post in order to find out how to change registered mobile number in gmail.
Steps to change the Registered Mobile Number in Gmail
Step 1: Open your Gmail account (gmail.com) and fill in your login credentials such as User name and Password.
Step 2: Click on a thumbnail of your icon on the right side of the top menu bar, and then click on “Privacy” to update your registered Mobile number.
Step 3: Now click on visit “Google Account Settings” under “Tools & Information” option.
Step 4: Click on “Edit” at the bottom right side of the option “Phone” to change your registered mobile number.
Step 5: Again you have to edit your registered mobile number by clicking on “Edit” option.
Step 6: Click on “Update number” to update your Registered Mobile number.
Step 7: Type your new mobile number and click on “Verify”.
Step 8: In order to verify the number, Gmail sends you the Verification Code on your registered mobile number. Click on “Get code”.
Step 9: Enter your verification code and click on “Verify”.
Step 10: Now you have successfully changed your number. Check the box if you want to use this number to alert you of suspicious account activity. Click on “Continue”.
Step 11: Click on “Done” after changing your number successfully.