from cakemail.models import PatchContact

contact = api.contact.update(
    list_id=<list ID>,
    contact_id=<contact ID>,
    patch_contact=PatchContact(
        email='<new contact email address>'
    )
)

<?php

$contact = $api->contact->update([
    'list_id' => <list ID>,
    'contact_id' => <contact ID>,
    'patch_contact' => new \Cakemail\Lib\Model\PatchContact([
        'email' => '<new contact email address>'
    ])
])