It looks like you've provided a phrase that appears to be encoded with a (like Caesar cipher) or an atbash cipher .
t → s h → g m → l y → x l → k → "sglxk" — no, maybe not. However, let me test = shift left 1: thmyl mtsfh upx mhkr
– your phrase "thmyl mtsfh upx mhkr" has a rhythm like a known cipher: each letter shifted by -1 (ROT-25 / shift backward 1): It looks like you've provided a phrase that
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) maybe not. However