If you had chargeable itemised billing enabled for this time, download your bills and view them.
If not, you can't get this information directly - your phone's call log will show all dialled & received calls for however long it goes back.
An SAR request should give you this information but comes with a one-month lead time: https://ee.co.uk/help/cyber-security/getting-started/request-my-personal-data
