The only time I can remember an attempt at a Philadelphian accent in a movie is in A History of Violence, and they didn't really get it. To be honest, this doesn't seem too bad to me. A Philadelphian accent doesn't have very much recognition generally, so why bother trying to be accurate about a detail that would really just distract and confuse an audience.
Concerning the recognition of a Philadelphian accent, I've recently realized that there is an excellent exemplar out there in the media, who is particularly loud, still very Philadelphian and maybe you've already heard him, thus making him the real topic of this post.
If you ever have trouble imagining what Philadelphians sound like, just think of Chris Matthews. Here is a video of Chris Matthews apologizing for some comments he made about Hillary Clinton. I'll give you a cursory tour of his accent, so that you'll know what to listen for. Really, there's no deep content here other than my own enthusiasm about my own dialect, but it's my blog so I won't be (any more) apologetic.
- [a]/[ɔ]: Of course, Matthews does not have the low back merger. It's very obvious throughout, so I won't give specific times to watch. The important lexical item is "on" which Matthews pronounces as [ɔn] near 00:19. This is a dead give away, since further south /ɔ/ develops a glide, like [aʊ], and further north they say [an]
- Dark [l]/ [l] Vocalization: Nearly all word final and pre-consonantal [l]'s are dark throughout the English speaking world, and in many places it is completely vocalizing. Philadelphia is has the same thing going on, but also intervocalically and in initial clusters. Matthews' l's are all very dark, and the most striking token of l-vocalization is at 02:48, where he has absolutely no [l] in Hillary, and also "television" at 01:17.
- [ar]->[ɔr]: This is a slightly different phenomenon. In Philadelphia, what would usually be realized as [ar] in other dialects is realized as [ɔr]. I believe it;s particularly pronounced in monosyllables, like "Hard" at 01:16 and "heart" at 01:19.
- Marry~Mary~Merry: Philadelphians pronounce these all distinctly, and while Matthews doesn't line them all up for us at any given point, "embarrassed" at 02:07 clearly has [ær].
- furry~ferry merger: Oddly enough, Philadelphians merge "ferry" and "furry", as can be heard when Matthews says "America" with [ʌr] at and "very" at 04:28
- aw raising: As I mentioned here, /aw/ in Philadelphia is produced more like [eɔ], as can be heard in numerous places in Matthews' speech.
- [ey] Lowering: Word finally, [ey] is lowered in a Southern kind of way, so it's more like [æy], like "day" at 00:14.
- [ay] Raising: [ay] is raised and backed before voiceless consonants, like in "night" at 00:18.
- [uw] and [ow]fronting: [uw] and [ow] are front of center for most of Matthews' words, especially "know" at 01:26 and "route" at 02:43. Fronting is blocked by a following [l] though, like in "poll" at 02:28