I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
Your phormium is most likely just struggling with some transplant shock. This is a stressful time of the year for a new transplant. I would not plant it deeper. You planted it properly based on the description you gave. Keep the soil moist but not soggy wet. I think it will pull out of it and be fine.
Thanks for the question. Please stop in again soon!
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