"Your plan covers fewer phones than are linked, so this phone uses the free features. Protection on the phone works as usual." appears when more phones are linked to your account than your plan covers, usually after a plan change (for example from Family, with 3 phones, to Plus, with 1).
The phones that were linked first keep the plan's features; the others use the free features. Protection works as usual on all of them.
To choose which phone keeps the plan: sign in at 1kr.uk, open Phones, and remove the phones you don't need. The next phone in line then gets the plan's features.
To cover more phones, choose a plan with more phones (Family covers 3) on the website.