Given the rest, maybe lbt is a typo for "lng" (long) or "lgt" (light). But it's lbt.
But more likely “thmyl” = "the mill" — (th e m i ll) → thmyl (y=i) thmyl lbt batl fyld dyzrt kwmbat
But “batl” = battle (missing vowels: b a t t l e → batl) “fyld” = field (f i e l d → fyld — y=i) “dyzrt” = desert (d e s e r t → dyzrt — y=e, z=s) “kwmbat” = combat (c o m b a t → kwmbat — kw for 'c' sound, m,b,t present). Given the rest, maybe lbt is a typo
But I think the intended original phrase is: Yes: "mile-long" = thmyl lbt → lbt = long? l o n g = l n g — not b. Unless 'b' stands for 'ng'? No. But I think the intended original phrase is:
Given all — most plausible decryption: — lbt = about? 'a b o u t' → abt, but lbt could be “el-bee-tee” → LB T = "lob tomb"? But I think the cleanest proper piece is to rewrite it into standard English by reversing the cipher: If we assume the cipher is: remove all vowels except 'y' can be 'i' or 'e', 'z' = s, 'kw' = c, 'bt' = tt?
So original: "The mill light battle field desert combat" — still nonsense.