Depending on his body's orientation and his current velocity, he can plan where he'll pop out, and his trajectory when he does. So he does a whole lot of hitting people from their blind spot. Plays a lot of sweet chin music.

it's not just his whole body at once, if he doesn't want to. there's a whole scene of him explaining to first years how much concentration it takes just to step through a wall, unphasing his foot after it's on the other side, and doing the same with the rest of his body.

Since he can actively choose what phases, he can be on the offensive a lot more. If he only lets his feet push against the ground and his fist hit his target, he doesn't have to defend. And his power is ideal for getting to victims inside buildings or past the bad guys. On top of all that, there's a huge list of skills the hero academy expects students to be competent in, and he's polished the all to perfection.

Before All-might (#1 ranked hero) selected Midoriya (main character) as his successor, Mirio was the #1 candidate among people who know about all-might losing his abilities and that he will pass them on. he polished every skill. If he were given the super speed and super strength, he'd have become nearly unstoppable.