I have to say I'm not a fan of this healing system...It was fine in Demons because so many enemies dropped them and there were varying strengths..Every 2nd boss I need to stop for 2 hours to farm more phials, made far worse by the massive load times.
Go to Central Yharnam lamp and run through the house to the bridge. Kill the fatty and werewolves, go back down through the house, killing fatties outside, down the elevator across the bridge and kill everything there. You should be close to max vials after one run. You can suicide off the ledge at the end to go back and do it a couple more times. Takes 5-10 minutes depending on the number of runs you do.