There's a set of rocks against the wall by the mushrooms at the room's entrance. Space jump on the one Samus is aiming at with R in this picture.

After landing on it, the next place to go is literally right above you. There's another place you can land on against the wall, but if you just space jump straight up Samus won't reach it, she'll just hit her head. Turn to face the track, then l-lock the view and jump off the rock. Use your second jump and move back to it less than a second later.

You should then land at a higher spot than the rock, yet still against the wall. If you landed at the right place, your view of the room when facing the track should now look like the below picture.

Now the horizontal piece of the track is easily within space jump distance, so land on it and space jump to the ledge you would normally grapple or l-lock space jump from to get over the phazon pit.

The method involving the phazon is faster but requires taking damage from it if you don't have the phazon suit yet. Go in the pit and notice how there are a few pieces of phazon that stick out of the ground. The one you want to jump on is in this picture.

Once on it, l-lock space jump from it to land safely on the ground above the other side of the pit. You have to do this almost perfectly or you'll miss and fall back in. Using this method in low % games before the phazon suit isn't a good idea unless you know what you're doing, because missing the jump once or twice will kill you.