Yes, it's a phase. Both of my kids went through it, one worse than the other. If he is just now starting to throw tantrums, count yourself lucky! Even though these tantrums are mystifying and frustrating to watch as a parent, there is no way to get around it. For most kids, they are so curious about the world around them at this age, and are really starting to notice what everyone around them is doing. They want to try everything they see, and they are just not coordinated enough to do everything! It's really frustrating for them, but this frustration is what pushes them to try again and get better, and eventually accomplish the task. At the same time, they are becoming independent, and so being told what to do all day every day is frustrating to them. They want to eat ice cream for lunch, and it's absolutely infuriating when Mommy tells them no! Or, they want to keep playing, but it's naptime and that's infuriating too! Well - the only way they learn how normal people act is for their parents to guide them. They won't always like it, but it's necessary.
What I learned with my two girls was that in general, when they had a tantrum about something that just seemed ridiculous, it was probably just the straw that broke the camel's back. At that point, there is absolutely nothing you can do to stop the tantrum because it is caused by built-up frustration. What I would do is calmly pick up the child and put them in the middle of their room and tell them, "When you are feeling better you can come out." and then leave the room. Sometimes the child felt better in 2 minutes - sometimes it took 20 minutes. Sometimes they fell asleep in the middle of the floor, or decided to play with their toys instead of coming out. The point is, they need some time to get rid of their frustration and get themselves under control. My almost-4 year old will actually go to her room on her own now when she is feeling frustrated - she'll start to get really mad and then announce, "I need to go to my room until I feel better!" - so it seems to work for us. =)
Hang in there - the terrible twos will be over before you know it!