I'm not exactly sure what a PCMHW is/does, but I'm guessing they are similar to support workers / healthcare assistants / nursing assistants but with a more specific focus and training. You'll have to research them.
but PWP's are part of Improving Access to Psychological Therapies (IAPT). You do a one year university course to become accredited and can then go on to do CBT therapist training. IAPT is essentially the gateway to mental health for the wider population - depression, anxiety, phobia etc. You do face to face and phone sessions with people, delivering session based CBT work.