Hello
Thank you for your question and reaching out. I can understand you are having query\issues related to change phone number in Outlook profile.
Open the Outlook website https://Outlook.com or https://mail.live.com
Click on your profile icon in the upper right corner of the screen to open Account Manager -> Select choose My Profile. -> Your Info -> Edit Account info -> Click Add Phone Number.
If you can’t add your phone number to your account, your best option is to contact Microsoft Support and try to get additional assistance. https://support.microsoft.com/home/contact
--If the reply is helpful, please Upvote and Accept as answer--