In this paper, we study the ideal approximation theory associated to almost $n$-exact structures in the $n$-exangulated category. The notions of $n$-ideal cotorsion pairs and $n$-$\mathbb{ F}$-phantom morphisms are introduced and studied. In particular, let $\mathscr{ C}$ be an extriangulated category which satisfies the condition (WIC) and $\mathcal{ T}$ be a nicely embedded $n$-cluster tilting subcategory of $\mathscr{ C}$, we prove Salce's Lemma in $\mathcal{ T}$.
Categories: math.CT