Call Recordings are principally legislatively controlled already by the The Telecommunications (Lawful Business Practice) (Interception of Communications) Regulations 2000; often referred to us the "Lawful Business Regulations". In summary these state that you can only record a call under one of these circumstances:
Most importantly, the same regulations state that reasonable efforts must always be made to ensure the caller and callee both know their call is being recorded or monitored.
The addition of the (GDPR) simply means any personal data recorded and/or monitored is even more tightly controlled. It's vital you have procedures and steps in place to contract whom has access to that Call Recording data, how it is stored and how you are protected in the event of data theft.