"Chief" George Phillips has his hands full. He's the man responsible for piloting the boat carrying Willard into Cambodia. He didn't realize he had to transport Willard beyond the legal borders of the war, but he agrees to it. He's not happy about it. You can see him seething throughout the trip upriver. His character is the jaded, tough soldier who just follows orders but isn't afraid to talk smack to his superiors if he thinks they deserve it.
Mainly, we just see Chief shouting orders at the other guys on the ship. He doesn't get any monologues or famous lines. But we get the sense that he has a compassionate side to his personality. When the other guys on the boat accidentally shoot a Vietnamese woman who they thought was trying to attack them, even though she was just attempting to protect a puppy, Chief wants to take the wounded girl to get medical attention. She's probably mortally wounded, though, so Willard just shoots her. Otherwise, it would've disrupted his mission. Very inconvenient.
Later, Kurtz's army attacks the members of the crew. Even though Kurtz's soldiers are just shooting toy arrows to warn them away, Chief doesn't tell his crew to stop firing real bullets back. This is a fatal miscalculation, as Kurtz's soldiers start throwing real spears.
Chief screams at Willard:
CHIEF: You got us into this mess and you can't get us out 'cos you don't know where the hell you're going, do you? Do you, you son of a b****, you f***!
Just then, Chief gets a spear straight through the chest.
When Willard goes to help him, Chief grabs him and tries to impale him on the spear point—he's outraged that Willard's mission has led to his own death. But Willard chokes Chief to death before Chief can kill him. Chief's death marks the passage into a more chaotic part of the film; he's been steering the boat, and you know what Willard says when you get out of the boat: you're on your own.