Hi Fahmeeda Yaseen,
It seems like this number is with RingCentral and you do not want to port it to another provider, that key challenge is ensuring that outbound calls made from Microsoft’s contact center solution display this number as the caller ID.
To Make a solution for this Microsoft Teams and Azure Communication Services (ACS) allow for outbound calls using custom caller IDs.
So, we need to configure direct routing or use operation connect integrate your existing RingCentral number with Teams. this setup allows outbound calls from Teams while showing the RingCentral number as the caller ID.
If Direct routing is not an option, then we can also check RingCentral offers SIP Trunking or an integration with Microsoft Teams, this will allow you to make outbound calls from Microsoft’s voice channel while maintaining your existing number.
If Direct routing supports, you can make setup as Caller ID policy to use custom outbound number using Microsoft Teams Admin Center.
https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan
https://learn.microsoft.com/en-us/microsoftteams/caller-id-policies
If the answer is helpful, please click Accept Answer and kindly upvote it so that other people who faces similar issue may get benefitted from it.
Let me know if you have any further Queries.