You can unlock a voucher when your loyalty balance reaches £5. You can earn voucher money through refer a friend and by leaving product reviews.
For each friend you refer you will receive £2.50 and for every successful Phase Zero product review you will receive £0.25. You simply need to reach £5 through either of these programs and your voucher code will be unlocked.
Each voucher code is unique to the account which it is applied too, and only one voucher can be used per purchase.