Explanation:

According to the Microsoft documentation1, you can use Audio conferencing policies to manage audio conferencing toll and toll-free numbers to be displayed in meeting invites created by users within your organization. You can use one of the two automatically created policies or create and assign custom policies. To create a custom audio-conferencing policy, you need to follow these steps1:
* In the left navigation of the Microsoft Teams admin center, go to Meetings > Audio conferencing.
* Select Add.
* Enter the name and description of the policy. The name can't contain special characters or be longer than 64 characters.
* Choose whether or not to Include toll-free numbers in meetings created by users of this policy.
* Under Phone numbers included in meeting invites, select Add phone number, and then select the toll- free number that you want to appear at the top of the list of numbers on Outlook invites to Teams meetings. You can also add other phone numbers that you want to include in the meeting invites.
* Select Save.
Therefore, based on this information, the correct sequence of actions is:
* Purchase Communication Credits.
* Request a service number.
* Assign a number to a resource account.
* Create and assign an Audio Conferencing policy.