Let F/Q(p) be a finite field extension, let k be a field of characteristic p. Fix
a Lubin Tate group Phi for F and let Gamma(circle) = Gamma x ... x Gamma with Gamma
= O-F(x) act on k[[t(1), ... , t(n)]][Pi(i)t(i)(-1)] by letting gamma(i) (in the i-th
factor Gamma) act on ti by insertion of ti into the power series attached to gamma(i)
by Phi. We show that k[[t(1), ... , t(n)]][Pi(i)t(i)(-1)] admits no non-trivial ideal
stable under Gamma(circle), thereby generalizing a result of Zabradi (who had treated
the case where Phi is the multiplicative group). We then discuss applications to (phi,
Gamma)-modules over k[[t(1), ... , t(n)]][Pi(i)t(i)(-1)].