  We consider the $\phi^4_1$ measure in an interval of length $\ell$, defined
by a symmetric double-well potential $W$ and inverse temperature $\beta$. Our
results concern its asymptotic behavior in the joint limit $\beta, \ell \to
\infty$, both in the subcritical regime $\ell \ll \rme^{\beta C_W}$ and in the
supercritical regime $\ell \gg \rme^{\beta C_W}$, where $C_W$ denotes the
surface tension. In the former case, in which the measure concentrates on the
pure phases, we prove the corresponding large deviation principle. The
associated rate function is the Modica-Mortola functional modified to take into
account the entropy of the locations of the interfaces. Further, we provide the
sharp asymptotics of the probability of having a given number of transitions
between the two pure phases. In the supercritical regime, the measure does not
longer concentrate and we show that the interfaces are asymptotically
distributed according to a Poisson point process.
