Where did the slang word phuba come from?

You might actually mean FUBAR. It is a vulgar acronym to mean something is really Fudged Up Beyond All Repair. (You might think up a slightly different version, but remember that this is a family friendly website.)

This phrase likely started in the military, except they might have said it meant Fouled Up Beyond All Repair. But like many official military abbreviations, it soon gained a somewhat vulgar informal meaning.