Why is Taiga afraid of dogs?
The Kuroko no Basuke wikia (unlike most wikias) is actually pretty good about citing its sources. The statement you quote includes a reference to chapter 74 (found in volume 9), page 9:



The left-hand speech bubble reads:


  When I was a kid back in the U.S., I got bitten by a giant dog, so [I seriously can't deal with them]...!


I don't believe this was mentioned in the anime, though. At minimum, Kagami doesn't say anything about it in episode 14, which is when the dog is introduced in the anime.