I crocheted myself a cellphone holder for a previous bag that I had, and have attached it to the booga bag I made.
I apologize for the quality of this picture -- but that's all I can do with the copier/scanner we have here at work... Basically I threaded the booga straps through the cellphone pocket I made and it just hangs inside my bag.
The cellphone pocket isn't felted -- its made with some acrylic craft yarn, that looks like the stuff they make "The Sac" from. To make the cellphone pocket I literally crocheted around and around my phone.
I did a chain stitch about 9 stitches long then a single crochet around both sides of the chain to start crocheting in the round. On each round I added a couple SC (single crochet) to each end to start making it wider and then placed my phone in what I'd made to see how much further I needed to expand before I started just going straight up.
When I got to the right height, I crocheted a strap to hang the pocket from and a flap to hold the phone in. (sorry for the sketchy instructions, but I literally just made it as I went). I'll try to get a better picture tonight.