The /f/ sound is spelled with <f> or <ph> in phase. The /j/ sound is spelled <y> throughout. The contrast can only occur initially.
The contrast is between a voiceless labio-dental fricative and a voiced palatal semivowel. It is not a problem.
The only aboo word pair is fuck/yuck.
Interesting pairs include:
The mean density value is 1.7%. The list makes 44 semantic distinctions, a loading of 63%.
fa yah fall yawl falls yawls far yah farrow yarrow fate Yate faugh yaw faugh yore faugh your faun yawn fauns yawns fawn yawn fawns yawns fawned yawned fawning yawning fear year fears years fee ye fell yell felled yelled felling yelling fells yells fellow yellow fellows yellows fen yen fens yens fend yenned fern yearn ferns yearns fey yea field yield fielded yielded fielding yielding fields yields fir year firs years fob yob fobs yobs focal yokel fogey yogi fogeys yogis folk yoke folks yokes folk yolk folks yolks fonder yonder food you'd for yaw for yore for your fore yaw fore yore fore your four yaw fours yaws four yore four your fours yours ford yawed fork York foul yowl fouled yowled fouling yowling fouls yowls fuck yuck fur year furs years furling yearling furlong yearlong phase yeas
John Higgins, Shaftesbury, October 2010.