Minecraft – How to turn an MCPE world into a .mcworld file

There are a couple of potential causes for this.

1. The area hasn't been loaded

The requirements for grass to grow have, from your screenshots, all been met. There is enough light and grass around for the grass to spread naturally. Sometimes one or two blocks might be a bit defiant, and refuse to spread, but with the amount you have, this is unlikely. The only other thing is that the area needs to be loaded. Chunk Loading means that if you are not in the area (for example, you might be in the Nether), that area is not loaded - which means all activity stops. Your crops don't grow, sheep don't regrow their wool, and the grass does not spread.

2. The dirt blocks you are using are Coarse Dirt

Coarse Dirt was added in version 1.7, and is almost identical to normal dirt blocks, save for a mildly different pattern, and the fact that grass will not grow on these blocks. However, if you use a hoe on these blocks, it will change it into normal dirt blocks (Added in 1.8). Grass can then grow on these blocks.

Yes, Minecraft Java edition and Minecraft bedrock/pocket/… edition are fundamentally different games and that will and can never change.

But you might still be able to run Minecraft Java servers on your iPhone, because that doesn't require being able to run the actual game. It's basically just a command line program written in Java, that's the most universally compatible program you can think of. On Android, I would just tell you to open a terminal emulator, or, if that doesn't work, to use something like Termux, but I don't know how this works on Apple devices. At least a "jailbreaked" iPhone will surely also be able to run a terminal emulator, if not a regular one as well. In that, you should be able to run the server like on a computer.

The only part that is device specific is port forwarding and getting a fixed IP for a device. But that depends on the model of router, not the phone model. It should still work the same for your phone.

Obligatory warning: Phones are not desktop computers, you will have terrible performance. Not even a Raspberry Pi can run a Minecraft server properly, a phone will likely be even worse at this.