As I said, there are other things Phil learns too - it is implied that Phil has learned French when he recites French poetry to Rita - but then, at this stage in the film, Phil has shown that he is more than willing to use deception to get into her knickers, so what's to say that he didn't simply spend a couple of days learning how to perfectly recite the one passage he picks to impress Rita. But that's probably nit-picking, so let's accept that he took lessons (given that Ramis himself also confirmed that Phil learned the language, and that the script confirms it below).
Rita: Believe it or not, I studied nineteenth-century French poetry. Phil: Rita: You speak French? Phil: Oui.
So, taking into account the fact that America only has about 1.6million French speakers, and isn't strictly speaking a Francophone nation, and the fact that Pennsylvania had no historical French settlement it would presumably have been more difficult for Phil to learn the language than it would somewhere with a large French speaking community.
With that in mind and also the fact that Phil is an adult learner, and thus less susceptible to learning a second language quickly, a conservative estimate, based on the idea of him taking lessons everyday (he clearly really wants to impress Rita), it would have taken somewhere around 12 years to become completely fluent (though ex-pats living in Francophone countries sometimes state it takes longer even than that) bringing the running total to: 12,315 days
Not only does Phil learn things to woo Rita - he also became all selfless, as indicated by this quote from Felix's Wife:
Dr. Connors. I want to thank you for fixing Felix's back. He can even help around the house again.
Hang on, he fixed his back?! When exactly did he find the time to learn enough in the medical field to "fix" the back of a man so incapacitated that he couldn't even help around the house?! Oh yeah, right, stuck in an infinite circle of time!
Well, I wouldn't think he had actually gone to Medical School (there isn't one in Punxsutawney - and he'd just end up doing first-day induction over and over anyway) or the required four years post-graduate studying to become a chiropractor, but you have to wonder how long it would take an unqualified TV presenter to master chiropractory to that level - or at least enough to wing it (it's a giant law-suit waiting to happen).
This one has to be pure speculation - though I did find a useful, teach yourself chiropractory video, of 100 minutes, which you'd think Phil would have to watch at least five or six times to learn off by heart (a low number since he would have some familiarity with learning lines quickly). It's probably also reasonable to suggest that Phil would have read up on the subject before attempting to administer off-the-cuff medical attention on a frail-looking elderly gentleman - say 20 days to be safe.
Adding the time it took to source the video (no more a suspension of belief required than his acquiring WWF tickets!), and the probable few times he practiced on Felix and it didn't quite work out as planned (and assuming each failed attempt then spoiled his entire day), I'd say a very rough bare minimum estimate of 26 days to learn to fix Felix's back.
So, so far that's: 12,341 days
I've already stated (in the disclaimer above) that these periods of learning could overlap - but really, I'm not entirely sure they would: clearly, you couldn't learn to play the piano after spending a few hours learning to sculpt ice (which would necessarily be a morning activity, given the lower temperatures and appropriate lighting).
And further, given Phil's professed dedication to each subject (his spending six months learning to throw cards into a hat proves an invaluable bench-mark), I don't think it likely that he would learn each thing in one long, crammed period of time. You have to remember, at the stage he is learning piano and ice sculpting, he has seemingly abandoned his desire to leave Punxsutawney, and is revelling in the infinite possibilities for self-advancement. So there.
Anyway, ignoring for a minute the good that he does, Phil does himself some badness too. Chief among them naughty activities, he robs a security van outside the bank, thanks to a Rain Man style plan:
Phil: A gust of wind. Phil: A dog barks. Phil: Cue the truck. Phil: Exit Herman; walk out into the bank. Phil: Exit Felix, and stand there with a not-so-bright look on your face. Phil: All right, Doris, come on. Hey, fix your bra, honey... That's better. Phil: Felix. Phil: How ya doin' Doris? Phil: Can I have a roll of quarters? Phil: Phil: 10, 9, 8, car... Phil: ...6, 5, quarters... Phil: ...3, 2... Herman: Felix, did I bring out two bags or one? Felix: I dunno.
That impressive knowledge, perfect to the exact minute detail, seemingly implies an extended period of research, including failed attempts (presumably also including him being run over by the car), which could not have been feasibly shorter than six weeks in my opinion. And I'm the one with the keyboard here- so six more weeks it is: Running total: 12,383 days
The final stage of this whole operation is breaking down what Phil achieves in his final Groundhog Day, and working out how long each soul-saving gesture would have taken...