That's awesome! I love it!
Would you be willing to share the pattern??
Sorry this is so late, I forgot to reply! If I make another one, I'll write the patern down.
This is approximately what I did:
Single crochet a rectangle large enough to wrap around your phone tightly. I slip-stitched the side, but sewing the seam up with yarn would look neater.
Flap: SC a rectangle for the flap starting in the appropriate place on your body rectangle. Make it as long as you want, leaving a small buttonhole (just chain stitch for a couple of stitches in the appropriate place, then continue the next row as usual). The flap on mine is actually another rectangle, even though it looks angular at the bottom - that's just because of the button.
Bottom: I wanted the bottom of the cozy to have dimension (my cell phone is chunky, not flat), so I crocheted a small oval and attached it as the bottom, but you could also just seam up the bottom two sides.
Eyes: I just used embroidery floss to make the whites and attached small black beads to that.
Tentacles: There are actually 8. Chain a length about 1/3 longer than you want your tentacles to be. Then start SC or DC. The pattern is sort of random, but the idea is that every couple of stitches, you SC or DC 2-3 stitches in one. Do this more often at first and then taper off toward the end. If you do it in every one, they will be more curly. For a more specific idea of how to do this, google the Caron "ruffle scarf" pattern.
Hope that helps!