– your phrase "thmyl mtsfh upx mhkr" has a rhythm like a known cipher: each letter shifted by -1 (ROT-25 / shift backward 1):

Try (Caesar shift +3): t → w h → k m → p y → b l → o → "wkpbo" no.

t(20) +5 = 25 → y h(8) +5 = 13 → m m(13) +5 = 18 → r y(25) +5 = 30 mod26 = 4 → d l(12) +5 = 17 → q → "ymrdq" (no)

"thmyl" t-1 = s h-1 = g m-1 = l y-1 = x l-1 = k → "sglxk" no.

It looks like you've provided a phrase that appears to be encoded with a (like Caesar cipher) or an atbash cipher .