Hi Sanjeewa Saman,
Thanks for reaching out to Microsoft Q&A.
You need to contact our support via one of the contacts mentioned here: https://support.microsoft.com/en-us/topic/global-customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2
This issue with phone number validation during Azure subscription sign-up can be addressed by submitting a support ticket and collaborating with our Azure subscription team.
Kindly Create a support ticket here and let us know once issue is fixed.
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.