Step 1:
The flower paper is about 6x6 inches.

Step 2:
This is the other side.
Fold over these four lines.

Step 3:
Turn the paper.

Step 4:
Fold this spot to the left

Step 5:
Fold five more spots to the left

Step 6:
This is how the model looks now.

Step 7:
Hold the model in one hand and pull / curve the petals outwards with your other hand.

Step 8:
Make three flowers like this one.

Step 9:
Make about 12 large leafs.
Click here for folding instructions of the leafs
Use paper of about 6x6 inches

Step 10:
This is the thick stem for the amaryllis flower.
Click here for instructions to make the stem
The used papers are also 6x6 inches

Step 11:
This is what you'll need for making a complete origami amaryllis:

3 large flowers
about 12 leafs
a thick paper stem
a small glass vase

Step 12:
Glue the flower to the top of the stem.

Step 13:
Glue to other two flowers to the stem.

Step 14:
The stem with flowers is done now....

Step 15:
Place the leaves in the vase and insert the stem with flowers in it too. If the stem is to short for the vase, you can just make the stem of a longer piece of paper or put a large paper ball in the bottom of the vase.

DONE!
This is a video tutorial for folding the Amaryllis: