For example, if you were to buy one ticket from LAX-EWR-LAX the roundtrip distance is about 4,888 miles and you would earn 1,629 Flight Points. To use these Flight Points you would need to spend $1,629 on which you would effectively earn two Thank You points per dollar, one point for the spend, and one point for the Flight Point match.
I don't think that's exactly right based on my experience.
If you bought a ticket from LAX-EWR-LAX (4,888 miles) you would earn 4,888 flight points + purchase points for the cost of the flight.
If the cost of the flight was $500, you would have 500 purchase points, which would be matched with 500 of the miles you flew.
To "release" the remaining 4,388 miles, you would need to spend/earn another 4,388 purchase on the card (can be a combination of your sign-up bonus, purchases and bonus purchase points).
EDIT: I overlooked the part where we were discussing the PremierPass card, not PremierPass Elite. Thanks for correcting me, mia and virmaior!