[Groundhog Day] Ned Ryerson is the devil, and imprisons Phil Conners in the time loop when Phil refuses to purchase Ned's insurance. The only way Phil escapes is by finally agreeing to buy it.

First and foremost:

When Phil first encounters Ned he insults him. Immediately after the insult Phil steps into a puddle, and Ned remarks, "Well-ha-ha! Watch out for that first step, it's a doozy!"

The "first step" Ned refers to literally the first step Phil takes after being placed into the time loop, and Ned is laughing at the irony that Phil's first step was so unpleasant. It's a cruel irony that only Ned is fully able to enjoy.

Secondly:

On the last day of the loop we see that Phil has purchased insurance from Ned, much to Ned's pleasure. This is actually the act that frees him from the time loop, not him successfully getting Rita sexually interested in him.

A tertiary point:

Immediately after Phil takes his "first step" into his hellish torment, the framing of the shot prominently shows a red coffee cup with steam coming off it as Ned laughs devilishly. http://i.imgur.com/IL0ti5t.jpg. Perhaps this symbolizes the firey torment of hell, directed at Phil as Ned points his finger at him.

Further corroborating that this is religious symbology...note the framing when Ned finally releases Phil from his perdition: http://i.imgur.com/Avvvil7.jpg

Phil's head is illuminated in a halo of light reminiscent of the Christ, and the groundhogs appear above his head in a Holy cross.

Edit: A point that just occurred to me:

Consider this: in this day and age, buying a shit-ton of life insurance is as close as you can get to selling your soul to someone.

Summary:

Phil's journey didn't involve his betterment as a person or getting Rita interested in him. Instead he was cast into damnation by Ned when he insulted him and refused his insurance, and he was absolved of his sin when he finally bought it and treated him respectfully.