Lynda Thornton wrote:
I've got some copper tape which I've used before to construct barriers,
but this plant is quite large and I don't think it will be very easy to
stop slugs etc climbing up the leaves from elsewhere or up through the
soil underneath, but I might try it to see if it has any effect.

Good luck! I find investing in the copper metal rings rather than the
tape is good value really. They get a lovely greyish colour eventually
and kinda blend in the garden. Cutting a few low branches of your
phormium would minimise climbing slugs.