gh cannot have an "F" sound at the beginning of a word (give just one example)
ti cannot have an "SH" sound at the end of a word (give just one example)
It is true that GH can have an "ef" sound at the end of a word as in "rough" ,"cough" ,"laugh", etc. GH can also have an "ef" sound in the middle of a word as in "roughage" and "laughing". However, GH never has an "ef" sound at the beginning of a word. It cannot be used that way. It is always preceded by a vowel!
In short, even in the world of irregular English spelling, you cannot spell fish "ghoti" any more than you can spell it "OLJHGOIUZXX". The latter makes just as much sense as the former.
You could spell fish "phoche" (PHoto wOmen quiCHE), but why would you want to?