The spelling of /b/ is always either <b> or <bb>. The /f/ sound is <f> or <ff> and occasionally <ph> as in camphor.
The contrast is between a voiced plosive and a voiceless fricative. Although they are fairly close in the mouth. I have never heard of it being a problem.
One taboo word pair is buck/fuck.
Interesting pairs include
The mean density value is 5.5%. The list makes 259 semantic distinctions, a loading of 49%.
aboard afford abrade afraid alb Alf B fee baa fa baa far baas farce babble baffle babbled baffled babbles baffles babbling baffling babel fable babels fables baboon buffoon baboons buffoons backed fact bad fad bag fag bagged fagged bagging fagging bags fags bail fail bailed failed bailing failing bails fails bait fate baits fates baited fated bait fête baited fêted baiting fêting baits fêtes bake fake baked faked bakes fakes baking faking bale fail bales fails baled failed balk fork balked forked balking forking balks forks ball fall balling falling balls falls balm farm bane fain ban fan banned fanned banning fanning bans fans bang fang bangs fangs bantam phantom bantams phantoms bar far bare fair bares fairs barer fairer barest fairest bare fare bared fared bares fares baring faring barely fairly barrier farrier barriers farriers barrow farrow barrows farrows base face based faced bases faces basing facing baser facer bass face basses faces bat fat bats fats batted fatted batting fatting bate fate bates fates bated fated bate fête bates fêtes bated fêted batten fatten battened fattened battening fattening battens fattens batter fatter batty fatty bawd ford bawds fords bay fey bays phase bays baize bayed fade be fee being feeing bear fair bears fairs bear fare bearing faring bears fares beard feared bearish fairish beast feast beasts feasts beau foe beaux foes beaver fever beavered fevered beavers fevers beckoned fecund bed Fed bee fee bees fees beer fear beers fears beetle fetal Bella fellah bell fell belled felled bells fells belling felling belle fell belles fells bellow fellow bellows fellows belt felt ben fen bens fens bend fend bended fended bending fending bends fends Bern fern Bernie ferny berry ferry berries ferries berth firth berths firths betted fetid better fetter bettered fettered bettering fettering betters fetters beys phase beys baize bhang fang bhangs fangs bib biff bibbing biffing bibs biffs bibbed biffed bib fib bibbed fibbed bibbinbg fibbing bibs fibs bier fear biers fears big fig bigger figure bight fight bights fights bile file bill fill bills fills lilled filled billing filling billet fillet billeted filleted billeting filleting billets fillets billy filly billies fillies binary finery bind find binding finding binds finds binder finder binders finders bine fine bines fines birth firth births firths bite fight biting fighting bites fights bitter fitter bitters fitters black flak blacks flax blade flayed blame flame blamed flamed blames flames blaming flaming blank flank blanks flanks blare flair blares flairs blare flare blared flared blaring flaring blares flares blaze flays bleat fleet bleating fleeting bled fled blemish Flemish blew flew blew flue blight flight blighted flighted blighting flighting blights flights Blighty flighty blip flip blips flips bloat float bloats floats bloated floated bloating floating bloc flock blocs flocks block flock blocked flocked blocking flocking blocks flocks blood flood blooded flooded blooding flooding bloods floods bloom flume blooms flumes blow floe blows floes blow flow blowed flowed blowing flowing blown flown blows floes blubber bluffer blubbers bluffers blue flew blue flue blues flues bluff fluff bluffed fluffed bluffing fluffing bluffs fluffs blurt flirt blurted flirted blurting flirting blurts flirts blush flush blushed flushed blushes flushes blushing flushing bluster fluster blustered flustered blustering flustering blusters flusters Blyth fly boar for boar fore boar four boars fours board ford boarded forded boarding fording boards fords bob fob bobbed fobbed bobs fobs bobbing fobbing bobbin boffin bobbins boffins bog fog bogs fogs bogged fogged bogging fogging bogey fogey bogeys fogeys boggy foggy boggier foggier boggiest foggiest boil foil boiled foiled boiling foiling boils foils bold foaled bold fold bolder folder bole foal boles foals bond fond bone phone boned phoned bones phones boning phoning bony phoney Bootle footle borage forage bore for bore fore bore four bores fours bored ford boss fosse bosses fosses bought fort bought fought boulder folder boulders folders bound found bounded founded bounding founding bounds founds boundary foundry boundaries foundries bounder founder bounders founders Bourne faun Bourne fawn bow foe bows foes bowled foaled bowled fold bowling foaling box fox boxed foxed boxes foxes boxing foxing boy Fowey brae fray braes frays braes phrase braid frayed braille frail braise phrase braised phrased braises phrases braising phrasing bran Fran bray fray braying fraying brayed frayed brays frays brays phrase bread Fred bred Fred Breda Freda breed freed breeze frees breeze frieze breezes friezes breeze freeze breezes freezes breezing freezing briar friar briars friars bride fried bridge fridge bridges fridges bright fright brighten frighten brightened frightened brightening frightening brightens frightens Brighton frighten brill frill brisk frisk broad fraud broads frauds broom Frome broth froth brought fraught brow Frau brown frown browned frowned browning frowning browns frowns bruit fruit bruited fruited bruiting fruiting bruits fruits brunt front brunts fronts buck fuck bucked fucked bucking fucking bucks fucks budge fudge budges fudges bug fug bugs fugs buggy fuggy bully fully bunk funk bunked funked bunking funking bunks funks bunny funny buoy Fowey burn fern burns ferns burnish furnish burnished furnished burnishing furnishing burns ferns burr fir burrs firs burr fur burrs furs burrow furrow burrowed furrowed burrowing furrowing burrows furrows burst first bursts firsts bury ferry burying ferrying buried ferried buries ferries bus fuss bused fussed buses fusses busing fussing busy fizzy busier fizzier busies fizzes busiest fizziest but phut butt phut buy fie buyer fire buyers fires buzz fuzz by fie bye fie cab caff cabs caffs camber camphor cob cough cobs coughs cobber coffer cobbers coffers cub cuff cubs cuffs deb deaf debase deface debased defaced debasement defacement debasements defacements debases defaces debasing defacing dibber differ dibbers differs double duffel ebb F ebbing effing football footfall footballs footfalls gab gaff grebe grief grub gruff hibernate hyphenate hibernated hyphenated hibernates hyphenates hibernating hyphenating hub huff hubby huffy loaf lobe nib niff ob off overblown overflown pub puff pubs puffs rabble raffle rabbles raffles rebuild refilled rib riff rub rough rubs roughs rubbing roughing rubbed roughed rubber rougher rubbish roughish rubble ruffle sabre safer scrub scruff scrubby scruffy scrubbier scruffier scrubbiest scruffiest snub snuff snubs snuffs snubbing snuffing snubbed snuffed sober sofa sobers sofas stub stuff stubbing stuffing stubbed stuffed stubs stuffs stubby stuffy stubbier stuffier stubbiest stuffiest sub sough subbing soughing subbed soughed subs soughs tabby Taffy tabbies Taffies trouble truffle troubles truffles tub tough tubby toughie wobble waffle wobbled waffled wobbles waffles wobbling waffling
John Higgins, Shaftesbury, January 2010.