I made one a few years ago now from a pattern on some sewing/crafty website. I thought I had bookmarked it and was going to pass it along but have yet to find it. But, what I modified the pattern to was to add a loop at the top of the back and purchased a 'clip'. I placed the loop fabric through the ring portion of the clip so that I can just clip the case to my belt loop. It's large enough for my phone and the pattern also called for a zippered portion on the front for credit cards, etc. It is my 'go to' wallet/phone case. I only use a purse when at formal-ish functions - never on a daily basis. And usually just carry cash in my pocket so rarely even use this as my phone usually fits in my back pocket. But it does live in my car as I now have my license and a few other necessary cards.
If I can figure out the website where I got the free pattern I'll happily post it as there were many great items/patterns.