Phone Numbers within Uptics are currently per 'User' account, hence if you buy a phone number under one account, another user under the same company will not be able to use it. You will need to purchase another number from the user's account itself form them to be able to make calls or send SMS.
In the near short-term future, we will be making some enhancements, adding some functionality inside sequences for SMS to be able to possibly rotate between any numbers purchased under the whole company account and not just your specific user profile.