The spelling of /p/ is always either <p> or <pp>. The /ʃ/ sound is usually spelled <sh> but we also see <ch> in chic and <ti> in cautious.
The contrast is between a stop and a fricative, both voiceless but fairly well separated in the mouth. It is unlikely to be a problem.
Interesting pairs include
corpus cautious
nappies gnashes
panties shanties
peppered shepherd
wrapper rasher
The mean density value is 2.9%. The list makes 149 semantic distinctions, a loading of 50%.
cap cache capped cached capping caching cap cash capped cashed capping cashing Capt cached Capt cashed clap clash clapped clashed clapping clashing cop cosh copped coshed copping coshing copies coshes Copt coshed corpus cautious cr^epe cr`eche crap crash crapped crashed crapping crashing dip dish dipped dished dipping dishing flap flash flapped flashed flapping flashing gap gash hap hash happed hashed happing hashing harp harsh harper harsher harpist harshest keep quiche knap gnash knapped gnashed knapping gnashing kopjes coshes lap lash lapped lashed lapping lashing leap leash map mash mapped mashed mapping mashing Marple marshal Marple martial nap gnash napped gnashed napping gnashing nappies gnashes P she P's she's pa shah pack shack packed shacked packing shacking packs shacks pact shacked pad shad paddock shaddock paddocks shaddocks pah shah paid shade pail shale pair share paired shared pairing sharing pairs shares pal shall pale shale pall shawl palls shawls Pam sham panties shanties par shah pars shahs pare share pared shared pares shares paring sharing park shark parks sharks parr shah parrs shahs parse shahs pat shat patter shatter pattered shattered pattering shattering patters shatters Paul shawl pause shores pave shave paved shaved paves shaves paving shaving paw shore pawed shored paws shores pawl shawl pawls shawls pawn Sean pawn shorn pax shacks pays chaise pea she peak chic peal she'll pealed shield pear share pears shares pearly Shirley peas she's pease she's peat sheet pee she peed she'd pees she's peek chic peel she'll peeled shield peeler Sheila peer shear peered sheared peering shearing peers shears peer sheer peered sheered peering sheering peers sheers peeves sheaves peke chic pelf shelf peppered shepherd perk shirk perked shirked perking shirking perks shirks perry sherry pert shirt Pete sheet pi shy pis shies pie shy pied shied pies shies pier shear piers shears pier sheer piers sheers pin shin pinned shinned pinning shinning pins shins pine shine pines shines pining shining pip ship pipped shipped pipping shipping pips ships pique chic pissed schist pit shit pits shits pitted shitted pitting shitting pitied shitted pock shock pocked shocked pocks shocks pod shod pole shoal poled shoaled poles shoals poling shoaling poll shoal poll shoals polled shoaled polling shoaling polish polyp pone shewn pooh shoe pooh shoo poor sure poorer surer poorest surest poorly surely poorness sureness pop posh popped poshed popping poshing pop shop popped shopped popping shopping pops shops poppies poshes poppas shoppers pore shore pored shored pores shores poring shoring porn Sean porn shorn port short ported shorted porting shorting ports shorts porter shorter portage shortage portages shortages portly shortly pose shows pot shot pots shots pour shore poured shored pouring shoring pours shores pout shout pouted shouted pouting shouting pouts shouts power shower powered showered powering showering powers showers pox shocks prank shrank primp shrimp primped shrimped primping shrimping primps shrimps prink shrink prinking shrinking prinks shrinks proud shroud Pru shrew prude shrewd puck shuck pucks shucks pud should pun shun punned shunned punning shunning puns shuns pun 'shun punt shunt punted shunted punter shunter punters shunters punting shunting punts shunts push shush pushed shushed pushes shushes pushing shushing putt shut putts shuts putting shutting putter shutter puttered shuttered puttering shuttering putters shutters pyre shire pyres shires pyre shyer rap rash sap sash slap slash slapped slashed slapping slashing slop slosh slopped sloshed slopping sloshing top tosh trap trash unpaved unshaved upper usher uppers ushers whelp welsh whelped welshed whelping welshing whip wish whipped wished whipping wishing whop wash whopped washed whopping washing whopper washer whoppers washers wrap rash wrapper rasher wrappers rashers