The /f/ sound is spelled with <f>, <ff>, <gh> in laugh or <ph> in Phil. The /ʧ/ sound is spelled <ch> or <tch>.
The contrast is between a labio-dental fricative and an alveolar affricate, both voiced. It is not a problem.
Taboo word pairs include fart/chart and fuck/chuck.
Interesting pairs include:
The mean density value is 3.1%. The list makes 96 semantic distinctions, a loading of 55%.
aft arched beef beech beefed beached beefing beaching biff bitch biffed bitched biffing bitching brief breach briefed breached briefing breaching caff catch effed etched effing etching F etch face chase faced chased faces chases facing chasing facer chaser facers chasers fad Chad fairy chary fain chain fair chair fairs chairs far char fare chair fared chaired faring chairing fares chairs farm charm farmed charmed farming charming farms charms farmer charmer farmers charmers fart chart farted charted farting charting farts charts fat chat fats chats fatted chatted fatting chatting fatter chatter fatty chatty fattier chattier fattiest chattiest faugh chaw faugh chore Fawley Chorley fear cheer feared cheered fearing cheering fears cheers fearful cheerful fearfully cheerfully fearfulness cheerfulness fearless cheerless fearlessly cheerlessly fearlessness cheerlessness fees cheese feign chain feigned chained feigning chaining feigns chains fellow cello fellows cellos feoff chief feoffs chiefs fern churn ferns churns ferry cherry ferries cherries fester Chester fickle chicle filed child fill chill fills chills filling chilling filled chilled filly chilli fillies chillies filly chilly filly Chile fine chine fines chines Finn chin Finns chins fin chin fins chins five chive fives chives fix chicks fizzle chisel fizzled chiselled fizzles chisels foes chose folk choke folks chokes food chewed fop chop fops chops for chaw for chore ford chawed fore chaw fore chore fork chalk forked chalked forking chalking forks chalks four chaw fours chaws four chore fours chores fox chocks fuck chuck fucked chucked fucking chucking fucks chucks fucker chukker fuckers chukkers fug chug fugs chugs funk chunk funks chunks funky chunky funkier chunkier funkiest chunkiest furl churl furls churls gulf gulch hoof hooch huff hutch if itch kaffir catcher kaffirs catchers laugh larch leaf leach leafed leached leafing leaching muff much niff niche Phil chill pilfered pilchard reef reach reefed reached reefing reaching ref retch reft retched riff rich scoff scotch scoffed scotched scoffing scotching serf search sniff snitch sniffed snitched sniffing snitching sough such staff starch staffed starched staffing starching stiff stitch surf search surfing searching surfed searched swift switched tough touch toughie touchy toughies touches tuft touched unfeigned unchained waft watched whiff which whiff witch
John Higgins, Shaftesbury, October 2010.