I've been going around with a really shabby phone case for quite a while now. It suits me fine that way. I'm more a holes in the jeans kinda guy anyway. But when the duct tape from a previous reparation was starting to ware away and the glue was gumming up my fingers, I decided I needed a more drastic fix-it job this time.
I found this piece of PVC tarp some time back.....it must have been in 2016 by the looks of things. I thought it would come in handy at some stage. They've been making bags and wallets out of this stuff since the '90s. My wallet's holding out pretty well, as is my rucksack, so it turns out I'm using it for my phone case!
Originally, I was planning to replicate the flap and all its features using a double layer of the PVC all over the case and a cardboard core on the front and back leaving the spine thinner and therefore more flexible. But luckily I scrapped that idea as the PVC was stiff enough with just one layer on the spine. To the front I doubled it over and on the back I just stuck it to the back of the rubber case.

Step 1: Materials and Equipment

PVC Tarp
Contact Glue
Craft Knife
Ruler
Cutting Board
10 mm Hole Punch
Hammer
2 Clamps and Wooden Off-cuts

Step 2: Rip Off the Old Flap

It was well stuck on for being a fake leather, cardboard core, phone case. Anyway, I'm going to use it as a template for my new flap so I won't throw it away just yet.

Step 3: Glue the Double Layer

This is the first step of reconstructing the flap. But I'm sorry I don't have any more shots to ilustrate the process fully. I measured out double the width of my phone + the rubber case. Masked off the line and applied the glue. Wait 20 minutes for it to set then fold and press firm. I like to use contact glue alot it gives you alot of control. The PVC is hard to fold on itself without leaving a lip on the edge. Minimize this lip by pressing between blocks of wood using clamps.

Step 4: Trace the Outline and Start Cutting

Use the old flap to trace the position of the hole on to the new PVC flap. Line up the front edge which was created in the last step with the same edge of the old flap. Trace the hole with a pencil. Trace the outline and cut the three remaining sides.

Step 5: Cut the Camera Hole

Cut the rounded corners out with the 10 mm. hole punch and finish the job cutting the straight lines between corners with the craft knife

Step 6: Round Off the Outside Corners

I did this by hand with the craft knife.

Step 7: Prepare for Gluing

Mask off the areas for gluing with masking tape.
I altered a popsicle stick to act as a spatula for spreading the glue. Its almost as clever as the other use I've given these sticks in this other Instructable: Pocket Popsicle Flyer

Step 8: Glue Back to Rubber Case

Spread the glue on both surfaces and immediately remove the masking tape. Like before with the flap, let the glue set 20 minutes.
Stick the pieces together carefully, making sure they are well aligned, and press firmly. And its done!!!