When you refer to PhD, I assume you're talking about Doctorate in Clinical Psychology, right? I ask, as in the UK that's not a PhD (which is a research doctorate) it's a DClinPsy (which is a professional doctorate). It's a requirement for registering with the Health and Care Professions Council (HCPC) and actually becoming a Clinical Psychologist.
If that is your aim, then you need to gain Graduate Basis for Chartered Membership of the BPS (normally abbreviated as GBC). Your existing undergraduate degree doesn't confer that status, so you need to do one of two things:
1. Use the process detailed in the BPS website to gain GBC using your current undergraduate degree. That will involve them looking at the modules within that degree to establish whether or not it contains the required content. It may not. See the "Non-UK applicants" section of
this page for details.
2. Taking a BPS-accredited conversion course, which will be a Master's degree. This
will not be specific to Clinical Psychology, and is instead design to ensure that all the required core Psychology content has been covered. To find such courses, use
this page, and specify Conversion Programmes with a Status of Accredited.
However, before you embark on this journey, please read the "International Applicants" page,
here, on the Clearing House for Postgraduate Courses in Clinical Psychology website. Pay particular attention to funding and residency requirements.