Here is the full list of all 37 Phar Lap - there are Horse Racing Challenge achievements worth 1,000 gamerscore.
Won 250 races
Reached player prestige 20
Won 4 races when riding against Richard
Won after passing 5 horses in the final stretch
Owned a grade 10 horse
Owned a level 50 horse
Won 5 races in Online Racing mode
Completed a set of 3 races in Online Racing mode
Bred 100 horses
Trained horses 500 times
Bred 50 horses
Accumulated 1,000,000 Gold
Owned a level 25 horse
Won 10 races in a photo finish
Reached player prestige 10
Trained horses 250 times
Owned 12 horses
Won 50 races
Sold a horse worth more than 15,000 Gold
Owned a grade 5 horse
Bred 10 horses
Trained horses 50 times
Spent 10,000m in preferred position
Bred a stallion
Owned 6 horses
Owned a level 10 horse
Completed a round of Betting Party mode
Spent 5,000m in preferred position
Won 10 races
Won a race despite a win pay of 15.00 or worse
Owned 4 horses
Win 3 races in a row in Story mode
Reached player prestige 2
Bred a mare
Owned 2 horses
Owned a grade 2 horse
Completed a set of 3 races in Quick Race mode