What is the best way to deal with a 2.5 year old throwing tantrums, especially in public? Will this be a phase that will pass?

The best way is to bring them away from the crowd. Let them throw their tantrums first before really telling them what's right and wrong. Lastly, distract them with something they like, like snacks, sweets, pacifier, their smelly pillow etc. And don't worry, it's a growing up phase and it will definitely grew out!