⟨o⟩ almost certainly represents [ɔ] – Appendix E of The Lord of the
Rings describes it as the sound in English “for”. This means we should
use a phoneme [[O]], not [[o]]; we should also create our own phoneme
for this, since the one we inherit from Latin sounds much more like [o]
to me.

In Quenya, long ⟨ó⟩ (and, presumably, ⟨ô⟩) is, according to Appendix E,
“tenser and ‘closer’”, which presumably means [o]. (Online sources seem
to agree.) The Latin [[o:]] phoneme works well enough for this.

In Sindarin, ⟨ó⟩ has “the same quality” as ⟨o⟩ according to Appendix E,
so emit it as [[O:]] for [ɔː]. This sounds sensible enough te me.

I’m undecided whether “Lothlórien” should be in sjn_list, to pronounce
it with [oː] instead of [ɔː]. It’s composed of Sindarin “loth” and
Quenya “Lórien”, so that could potentially justify a pronunciation with
a Quenya ⟨ó⟩. But then again, maybe it should be a standard Sindarin
⟨ó⟩. For now, I’ve opted to not add it; in the film The Fellowship of
the Ring, Aragorn (Viggo Mortensen) says “Lothlórien” after the
Fellowship leave Moria, and to me his ⟨ó⟩ sounds more like [ɔː] than
[oː], so if this is wrong, at least it’s no more wrong than the famous
movie adaptation :)