Perhaps antique medical terminology entices you. An image of surgeons wearing ties is appealing; you see them gathered around a patient, whose lungs are laboured (his breath sounds like “ph, th, ph, th”). It’s some infection. The gentleman in charge lifts his stethoscope from the chest and pronounces, “This is not staph; this is phthisis.”
But how does he pronounce it? Is this a word like exophthalmic, where the lower lip and the tip of the tongue exchange fricatives against the teeth? That’s one option, yes. But although it’s no great problem to make that sound (stick a little hair on the tip of your tongue and see how many times you make it until the hair is gone), it’s not part of the normal phonotactics of English. So some drop the /f/. Some go further, making the onset a simple /t/. Oh, but what a crisp, delicate touch that is, a tip-of-the-tongue stop, so far removed from the fricatives – and making four letters represent a single short sound.
The back half of the word is agreed on, at least. The remaining two consonants are also voiceless fricatives: it’s pronounced like Isis, the name of the goddess, or like “Aye, sis.” So no matter how you do it, there is ample hissing – or wheezing – for your consumption.
And, indeed, consumption is another word that used to be used to describe the same thing that phthisis was most often used to describe: what now we call tuberculosis. But it has been used to describe other wasting diseases, particularly of the lungs, as it has been ever since it was a Greek word. (One thing’s for sure: if you have phthisis, you’re not just up shit creek, you’re on shit ship.)
There is one kind of phthisis that is not of the lungs, however, and it may be a bit ironic, given the superficial kinship of form between this word and exophthalmic: ophthalmologists may speak of phthisis bulbi (not related to Taras Bulba), which is an atrophy of the eye, involving shrinkage of the eyeball.