When Customers is enabled for a project, existing numbers are assigned to its protected Default customer. A new number also uses that customer when no other customer was selected during creation. This assignment does not mean the number was disconnected or transferred to another team.
Check the Customer field in the intended project. Customer identifies the person or business the number belongs to; Owned by identifies the Console or Inspector user controlling it. These fields describe different relationships. If the assignment is wrong, review it in that project or contact support before deleting a number to correct its grouping.