why do some say 'philadelthia' instead of 'philadephia'?

I've never heard that before. We natives prounounce it like this: Fl'delfya.

I'm wondering if you might be referring to an old joke about Philly. The term was "Filthy-delphia", which comments on the trash around the city.

I used to work as a clerk at a trucking service, and out-of-town truckers would refer to Philly that way. At the time I didn't think much about the comment, b/c a lot of the truckers made jokes about everything. But then, I moved out of state to go to college. And compared to the other cities where I've lived since, Philly does have a litter problem.

Lisp. Or, or is it similar to Noo Yoke, Noo Yoak? Neyo Yorrrk was from a Spanish speaking person.

It is so sad to hear that especially because it is such a beautiful rich city with so much potential! Articulation usually comes with education. Unfortunately, with some people it is a mis-pronunciation!

I have never heard that before. I have heard "filtadelphia" which refers to how dirty Philly can be; also I have heard "illadelphia" which was coined by The Roots; but I have never heard "philadelthia." Maybe that's just how some non-Philadelphians say it.

Ignorance.

I'm from Philly and I've never heard anyone pronounce it that way. But, we do call it Filthydelphia.

Ebonics

You mean Philamadelphia?

Never heard it that way